LibC: Reimplement scanf from the ground up

This adds support for some previously unsupported features
(e.g. length modifiers) and fixes at least one FIXME.
Fixes #90.

Userland/Libraries/LibC/scanf.cpp

@@ -1,227 +1,546 @@
 /*
- * Copyright (c) 2000-2002 Opsycon AB  (www.opsycon.se)
- * 
+ * Copyright (c) 2021, the SerenityOS developers.
+ * All rights reserved.
+ *
  * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- * 3. All advertising materials mentioning features or use of this software
- *    must display the following acknowledgement:
- *    This product includes software developed by Opsycon AB.
- * 4. The name of the author may not be used to endorse or promote products
- *    derived from this software without specific prior written permission.
+ * modification, are permitted provided that the following conditions are met:
  *
- * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
- * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
- * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
- * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
  *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
+
 #include <AK/Assertions.h>
+#include <AK/GenericLexer.h>
+#include <AK/LogStream.h>
+#include <AK/StdLibExtras.h>
 #include <ctype.h>
 #include <stdarg.h>
-#include <stdint.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 
-static const char* determine_base(const char* p, int& base)
-{
-    if (p[0] == '0') {
-        switch (p[1]) {
-        case 'x':
-            base = 16;
-            break;
-        case 't':
-        case 'n':
-            base = 10;
-            break;
-        case 'o':
-            base = 8;
-            break;
-        default:
-            base = 10;
-            return p;
-        }
-        return p + 2;
+enum LengthModifier {
+    None,
+    Default,
+    Char,
+    Short,
+    Long,
+    LongLong,
+    IntMax,
+    Size,
+    PtrDiff,
+    LongDouble,
+};
+
+enum ConversionSpecifier {
+    Unspecified,
+    Decimal,
+    Integer,
+    Octal,
+    Unsigned,
+    Hex,
+    Floating,
+    String,
+    UseScanList,
+    Character,
+    Pointer,
+    OutputNumberOfBytes,
+    Invalid,
+};
+
+enum class ReadKind {
+    Normal,
+    Octal,
+    Hex,
+    Infer,
+};
+
+template<typename T, typename ApT, ReadKind kind = ReadKind::Normal>
+struct read_element_concrete {
+    bool operator()(GenericLexer&, va_list)
+    {
+        return false;
     }
-    base = 10;
-    return p;
-}
+};
 
-static int _atob(unsigned long* vp, const char* p, int base)
-{
-    unsigned long value, v1, v2;
-    const char* q;
-    char tmp[20];
-    int digit;
+template<typename ApT, ReadKind kind>
+struct read_element_concrete<int, ApT, kind> {
+    bool operator()(GenericLexer& lexer, va_list* ap)
+    {
+        lexer.ignore_while(isspace);
 
-    if (p[0] == '0' && (p[1] == 'x' || p[1] == 'X')) {
-        base = 16;
-        p += 2;
+        auto* ptr = va_arg(*ap, ApT*);
+        long value = 0;
+        char* endptr = nullptr;
+        auto nptr = lexer.remaining().characters_without_null_termination();
+        if constexpr (kind == ReadKind::Normal)
+            value = strtol(nptr, &endptr, 10);
+        if constexpr (kind == ReadKind::Octal)
+            value = strtol(nptr, &endptr, 8);
+        if constexpr (kind == ReadKind::Hex)
+            value = strtol(nptr, &endptr, 16);
+        if constexpr (kind == ReadKind::Infer)
+            value = strtol(nptr, &endptr, 0);
+
+        if (!endptr)
+            return false;
+
+        if (endptr == nptr)
+            return false;
+
+        auto diff = endptr - nptr;
+        ASSERT(diff > 0);
+        lexer.ignore((size_t)diff);
+
+        *ptr = value;
+        return true;
     }
+};
 
-    if (base == 16 && (q = strchr(p, '.')) != 0) {
-        if (q - p > (ssize_t)sizeof(tmp) - 1)
-            return 0;
-        memcpy(tmp, p, q - p);
-        tmp[q - p] = '\0';
+template<typename ApT, ReadKind kind>
+struct read_element_concrete<char, ApT, kind> {
+    bool operator()(GenericLexer& lexer, va_list* ap)
+    {
+        static_assert(kind == ReadKind::Normal, "Can't read a non-normal character");
 
-        if (!_atob(&v1, tmp, 16))
-            return 0;
-        ++q;
-        if (strchr(q, '.'))
-            return 0;
-        if (!_atob(&v2, q, 16))
-            return 0;
-        *vp = (v1 << 16) + v2;
-        return 1;
+        auto* ptr = va_arg(*ap, ApT*);
+
+        if (lexer.is_eof())
+            return false;
+
+        auto ch = lexer.consume();
+        *ptr = ch;
+        return true;
     }
+};
 
-    value = *vp = 0;
-    for (; *p; p++) {
-        if (*p >= '0' && *p <= '9')
-            digit = *p - '0';
-        else if (*p >= 'a' && *p <= 'f')
-            digit = *p - 'a' + 10;
-        else if (*p >= 'A' && *p <= 'F')
-            digit = *p - 'A' + 10;
+template<typename ApT, ReadKind kind>
+struct read_element_concrete<unsigned, ApT, kind> {
+    bool operator()(GenericLexer& lexer, va_list* ap)
+    {
+        lexer.ignore_while(isspace);
+
+        auto* ptr = va_arg(*ap, ApT*);
+        unsigned long value = 0;
+        char* endptr = nullptr;
+        auto nptr = lexer.remaining().characters_without_null_termination();
+        if constexpr (kind == ReadKind::Normal)
+            value = strtoul(nptr, &endptr, 10);
+        if constexpr (kind == ReadKind::Octal)
+            value = strtoul(nptr, &endptr, 8);
+        if constexpr (kind == ReadKind::Hex)
+            value = strtoul(nptr, &endptr, 16);
+        if constexpr (kind == ReadKind::Infer)
+            value = strtoul(nptr, &endptr, 0);
+
+        if (!endptr)
+            return false;
+
+        if (endptr == nptr)
+            return false;
+
+        auto diff = endptr - nptr;
+        ASSERT(diff > 0);
+        lexer.ignore((size_t)diff);
+
+        *ptr = value;
+        return true;
+    }
+};
+
+template<typename ApT, ReadKind kind>
+struct read_element_concrete<float, ApT, kind> {
+    bool operator()(GenericLexer& lexer, va_list* ap)
+    {
+        lexer.ignore_while(isspace);
+
+        auto* ptr = va_arg(*ap, ApT*);
+
+        double value = 0;
+        char* endptr = nullptr;
+        auto nptr = lexer.remaining().characters_without_null_termination();
+        if constexpr (kind == ReadKind::Normal)
+            value = strtod(nptr, &endptr);
         else
-            return 0;
+            return false;
 
-        if (digit >= base)
-            return 0;
-        value *= base;
-        value += digit;
+        if (!endptr)
+            return false;
+
+        if (endptr == nptr)
+            return false;
+
+        auto diff = endptr - nptr;
+        ASSERT(diff > 0);
+        lexer.ignore((size_t)diff);
+
+        *ptr = value;
+        return true;
     }
-    *vp = value;
-    return 1;
-}
+};
 
-static int atob(unsigned int* vp, const char* p, int base)
-{
-    unsigned long v;
-
-    if (base == 0)
-        p = determine_base(p, base);
-    if (_atob(&v, p, base)) {
-        *vp = v;
-        return 1;
-    }
-    return 0;
-}
-
-#define ISSPACE " \t\n\r\f\v"
-
-int vsscanf(const char* buf, const char* s, va_list ap)
-{
-    int base = 10;
-    char* t;
-    char tmp[BUFSIZ];
-    bool noassign = false;
-    int count = 0;
-    int width = 0;
-
-    // FIXME: This doesn't work quite right. For example, it fails to match 'SSH-2.0-OpenSSH_8.2p1 Ubuntu-4ubuntu0.1\r\n'
-    //        with 'SSH-%d.%d-%[^\n]\n'
-
-    while (*s && *buf) {
-        while (isspace(*s))
-            s++;
-        if (*s == '%') {
-            s++;
-            for (; *s; s++) {
-                if (strchr("dibouxcsefg%", *s))
-                    break;
-                if (*s == '*')
-                    noassign = true;
-                else if (*s >= '1' && *s <= '9') {
-                    const char* tc;
-                    for (tc = s; isdigit(*s); s++)
-                        ;
-                    ASSERT((ssize_t)sizeof(tmp) >= s - tc + 1);
-                    memcpy(tmp, tc, s - tc);
-                    tmp[s - tc] = '\0';
-                    atob((uint32_t*)&width, tmp, 10);
-                    s--;
-                }
-            }
-            if (*s == 's') {
-                while (isspace(*buf))
-                    buf++;
-                if (!width)
-                    width = strcspn(buf, ISSPACE);
-                if (!noassign) {
-                    // In this case, we have no way to ensure the user buffer is not overflown :(
-                    memcpy(t = va_arg(ap, char*), buf, width);
-                    t[width] = '\0';
-                }
-                buf += width;
-            } else if (*s == 'c') {
-                if (!width)
-                    width = 1;
-                if (!noassign) {
-                    memcpy(t = va_arg(ap, char*), buf, width);
-                    // No null terminator!
-                }
-                buf += width;
-            } else if (strchr("dobxu", *s)) {
-                while (isspace(*buf))
-                    buf++;
-                if (*s == 'd' || *s == 'u')
-                    base = 10;
-                else if (*s == 'x')
-                    base = 16;
-                else if (*s == 'o')
-                    base = 8;
-                else if (*s == 'b')
-                    base = 2;
-                if (!width) {
-                    if (isspace(*(s + 1)) || *(s + 1) == 0) {
-                        width = strcspn(buf, ISSPACE);
-                    } else {
-                        auto* p = strchr(buf, *(s + 1));
-                        if (p)
-                            width = p - buf;
-                        else {
-                            noassign = true;
-                            width = 0;
-                        }
-                    }
-                }
-                memcpy(tmp, buf, width);
-                tmp[width] = '\0';
-                buf += width;
-                if (!noassign) {
-                    if (!atob(va_arg(ap, uint32_t*), tmp, base))
-                        noassign = true;
-                }
-            }
-            if (!noassign)
-                ++count;
-            width = 0;
-            noassign = false;
-            ++s;
-        } else {
-            while (isspace(*buf))
-                buf++;
-            if (*s != *buf)
-                break;
-            else {
-                ++s;
-                ++buf;
-            }
+template<typename T, ReadKind kind>
+struct read_element {
+    bool operator()(LengthModifier length_modifier, GenericLexer& input_lexer, va_list* ap)
+    {
+        switch (length_modifier) {
+        default:
+        case None:
+            ASSERT_NOT_REACHED();
+        case Default:
+            return read_element_concrete<T, T, kind> {}(input_lexer, ap);
+        case Char:
+            return read_element_concrete<T, char, kind> {}(input_lexer, ap);
+        case Short:
+            return read_element_concrete<T, short, kind> {}(input_lexer, ap);
+        case Long:
+            if constexpr (IsSame<T, int>::value)
+                return read_element_concrete<T, long, kind> {}(input_lexer, ap);
+            if constexpr (IsSame<T, float>::value)
+                return read_element_concrete<T, double, kind> {}(input_lexer, ap);
+            return false;
+        case LongLong:
+            if constexpr (IsSame<T, int>::value)
+                return read_element_concrete<T, long long, kind> {}(input_lexer, ap);
+            if constexpr (IsSame<T, float>::value)
+                return read_element_concrete<T, double, kind> {}(input_lexer, ap);
+            return false;
+        case IntMax:
+            return read_element_concrete<T, intmax_t, kind> {}(input_lexer, ap);
+        case Size:
+            return read_element_concrete<T, size_t, kind> {}(input_lexer, ap);
+        case PtrDiff:
+            return read_element_concrete<T, ptrdiff_t, kind> {}(input_lexer, ap);
+        case LongDouble:
+            return read_element_concrete<T, long double, kind> {}(input_lexer, ap);
         }
     }
-    return count;
+};
+
+template<>
+struct read_element<char*, ReadKind::Normal> {
+    read_element(StringView scan_set = {}, bool invert = false)
+        : scan_set(scan_set.is_null() ? " \t\n\f\r" : scan_set)
+        , invert(scan_set.is_null() ? true : invert)
+        , was_null(scan_set.is_null())
+    {
+    }
+
+    bool operator()(LengthModifier length_modifier, GenericLexer& input_lexer, va_list* ap)
+    {
+        // FIXME: Implement wide strings and such.
+        if (length_modifier != LengthModifier::Default)
+            return false;
+
+        if (was_null)
+            input_lexer.ignore_while(isspace);
+
+        auto* ptr = va_arg(*ap, char*);
+        auto str = input_lexer.consume_while([this](auto c) { return this->matches(c); });
+        if (str.is_empty())
+            return false;
+
+        memcpy(ptr, str.characters_without_null_termination(), str.length());
+        ptr[str.length()] = 0;
+
+        return true;
+    }
+
+private:
+    bool matches(char c) const
+    {
+        return invert ^ scan_set.contains(c);
+    }
+
+    const StringView scan_set;
+    bool invert { false };
+    bool was_null { false };
+};
+
+template<>
+struct read_element<void*, ReadKind::Normal> {
+    bool operator()(LengthModifier length_modifier, GenericLexer& input_lexer, va_list* ap)
+    {
+        if (length_modifier != LengthModifier::Default)
+            return false;
+
+        input_lexer.ignore_while(isspace);
+
+        auto* ptr = va_arg(*ap, void**);
+        auto str = input_lexer.consume_while([this](auto c) { return this->should_consume(c); });
+
+        if (count != 8) {
+        fail:;
+            for (size_t i = 0; i < count; ++i)
+                input_lexer.retreat();
+            return false;
+        }
+
+        char buf[9] { 0 };
+        memcpy(buf, str.characters_without_null_termination(), 8);
+        buf[8] = 0;
+        char* endptr = nullptr;
+        auto value = strtoull(buf, &endptr, 16);
+
+        if (endptr != &buf[8])
+            goto fail;
+
+        memcpy(ptr, &value, sizeof(value));
+        return true;
+    }
+
+private:
+    bool should_consume(char c)
+    {
+        if (count == 8)
+            return false;
+        if (!isxdigit(c))
+            return false;
+
+        ++count;
+        return true;
+    }
+    size_t count { 0 };
+};
+
+extern "C" int vsscanf(const char* input, const char* format, va_list ap)
+{
+    GenericLexer format_lexer { format };
+    GenericLexer input_lexer { input };
+
+    int elements_matched = 0;
+
+    while (!format_lexer.is_eof()) {
+        format_lexer.ignore_while(isspace);
+        if (!format_lexer.next_is('%')) {
+        read_one_literal:;
+            input_lexer.ignore_while(isspace);
+            if (format_lexer.is_eof())
+                break;
+
+            auto next_char = format_lexer.consume();
+            if (!input_lexer.consume_specific(next_char))
+                return elements_matched;
+            continue;
+        }
+
+        if (format_lexer.next_is("%%")) {
+            format_lexer.ignore();
+            goto read_one_literal;
+        }
+
+        format_lexer.ignore(); // '%'
+
+        bool invert_scanlist = false;
+        StringView scanlist;
+        LengthModifier length_modifier { None };
+        ConversionSpecifier conversion_specifier { Unspecified };
+    reread_lookahead:;
+        auto format_lookahead = format_lexer.peek();
+        if (length_modifier == None) {
+            switch (format_lookahead) {
+            case 'h':
+                if (format_lexer.peek(1) == 'h') {
+                    format_lexer.consume(2);
+                    length_modifier = Char;
+                } else {
+                    format_lexer.consume(1);
+                    length_modifier = Short;
+                }
+                break;
+            case 'l':
+                if (format_lexer.peek(1) == 'l') {
+                    format_lexer.consume(2);
+                    length_modifier = LongLong;
+                } else {
+                    format_lexer.consume(1);
+                    length_modifier = Long;
+                }
+                break;
+            case 'j':
+                format_lexer.consume();
+                length_modifier = IntMax;
+                break;
+            case 'z':
+                format_lexer.consume();
+                length_modifier = Size;
+                break;
+            case 't':
+                format_lexer.consume();
+                length_modifier = PtrDiff;
+                break;
+            case 'L':
+                format_lexer.consume();
+                length_modifier = LongDouble;
+                break;
+            default:
+                length_modifier = Default;
+                break;
+            }
+            goto reread_lookahead;
+        }
+        if (conversion_specifier == Unspecified) {
+            switch (format_lookahead) {
+            case 'd':
+                format_lexer.consume();
+                conversion_specifier = Decimal;
+                break;
+            case 'i':
+                format_lexer.consume();
+                conversion_specifier = Integer;
+                break;
+            case 'o':
+                format_lexer.consume();
+                conversion_specifier = Octal;
+                break;
+            case 'u':
+                format_lexer.consume();
+                conversion_specifier = Unsigned;
+                break;
+            case 'x':
+                format_lexer.consume();
+                conversion_specifier = Hex;
+                break;
+            case 'a':
+            case 'e':
+            case 'f':
+            case 'g':
+                format_lexer.consume();
+                conversion_specifier = Floating;
+                break;
+            case 's':
+                format_lexer.consume();
+                conversion_specifier = String;
+                break;
+            case '[':
+                format_lexer.consume();
+                scanlist = format_lexer.consume_until(']');
+                if (scanlist.starts_with('^')) {
+                    scanlist = scanlist.substring_view(1);
+                    invert_scanlist = true;
+                }
+                conversion_specifier = UseScanList;
+                break;
+            case 'c':
+                format_lexer.consume();
+                conversion_specifier = Character;
+                break;
+            case 'p':
+                format_lexer.consume();
+                conversion_specifier = Pointer;
+                break;
+            case 'n':
+                format_lexer.consume();
+                conversion_specifier = OutputNumberOfBytes;
+                break;
+            case 'C':
+                format_lexer.consume();
+                length_modifier = Long;
+                conversion_specifier = Character;
+                break;
+            case 'S':
+                format_lexer.consume();
+                length_modifier = Long;
+                conversion_specifier = String;
+                break;
+            default:
+                format_lexer.consume();
+                conversion_specifier = Invalid;
+                break;
+            }
+        }
+
+        // Now try to read.
+        switch (conversion_specifier) {
+        case Invalid:
+        case Unspecified:
+        default:
+            // "undefined behaviour", let's be nice and crash.
+            dbgln("Invalid conversion specifier {} in scanf!", (int)conversion_specifier);
+            ASSERT_NOT_REACHED();
+        case Decimal:
+            if (!read_element<int, ReadKind::Normal> {}(length_modifier, input_lexer, &ap))
+                format_lexer.consume_all();
+            else
+                ++elements_matched;
+            break;
+        case Integer:
+            if (!read_element<int, ReadKind::Infer> {}(length_modifier, input_lexer, &ap))
+                format_lexer.consume_all();
+            else
+                ++elements_matched;
+            break;
+        case Octal:
+            if (!read_element<unsigned, ReadKind::Octal> {}(length_modifier, input_lexer, &ap))
+                format_lexer.consume_all();
+            else
+                ++elements_matched;
+            break;
+        case Unsigned:
+            if (!read_element<unsigned, ReadKind::Normal> {}(length_modifier, input_lexer, &ap))
+                format_lexer.consume_all();
+            else
+                ++elements_matched;
+            break;
+        case Hex:
+            if (!read_element<unsigned, ReadKind::Hex> {}(length_modifier, input_lexer, &ap))
+                format_lexer.consume_all();
+            else
+                ++elements_matched;
+            break;
+        case Floating:
+            if (!read_element<float, ReadKind::Normal> {}(length_modifier, input_lexer, &ap))
+                format_lexer.consume_all();
+            else
+                ++elements_matched;
+            break;
+        case String:
+            if (!read_element<char*, ReadKind::Normal> {}(length_modifier, input_lexer, &ap))
+                format_lexer.consume_all();
+            else
+                ++elements_matched;
+            break;
+        case UseScanList:
+            if (!read_element<char*, ReadKind::Normal> { scanlist, invert_scanlist }(length_modifier, input_lexer, &ap))
+                format_lexer.consume_all();
+            else
+                ++elements_matched;
+            break;
+        case Character:
+            if (!read_element<char, ReadKind::Normal> {}(length_modifier, input_lexer, &ap))
+                format_lexer.consume_all();
+            else
+                ++elements_matched;
+            break;
+        case Pointer:
+            if (!read_element<void*, ReadKind::Normal> {}(length_modifier, input_lexer, &ap))
+                format_lexer.consume_all();
+            else
+                ++elements_matched;
+            break;
+        case OutputNumberOfBytes: {
+            auto* ptr = va_arg(ap, int*);
+            *ptr = input_lexer.tell();
+            ++elements_matched;
+            break;
+        }
+        }
+    }
+
+    return elements_matched;
 }

Userland/Tests/LibC/scanf.cpp

@@ -0,0 +1,253 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/Array.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+typedef long double longdouble;
+typedef long long longlong;
+typedef char charstar[32];
+
+template<typename T>
+constexpr static Array<unsigned char, 32> to_value_t(T x)
+{
+    // The endianness doesn't really matter, since we're going to convert both sides with this anyway.
+    union Value {
+        u8 v[32];
+        T t;
+    };
+
+    auto value = Value { .t = x };
+
+    return {
+        value.v[0],
+        value.v[1],
+        value.v[2],
+        value.v[3],
+        value.v[4],
+        value.v[5],
+        value.v[6],
+        value.v[7],
+        value.v[8],
+        value.v[9],
+        value.v[10],
+        value.v[11],
+        value.v[12],
+        value.v[13],
+        value.v[14],
+        value.v[15],
+        value.v[16],
+        value.v[17],
+        value.v[18],
+        value.v[19],
+        value.v[20],
+        value.v[21],
+        value.v[22],
+        value.v[23],
+        value.v[24],
+        value.v[25],
+        value.v[26],
+        value.v[27],
+        value.v[28],
+        value.v[29],
+        value.v[30],
+        value.v[31],
+    };
+}
+
+template<size_t N>
+constexpr static Array<unsigned char, 32> str_to_value_t(const char (&x)[N])
+{
+    Array<unsigned char, 32> value { 0 };
+    for (size_t i = 0; i < N; ++i)
+        value[i] = x[i];
+    return value;
+}
+
+struct Argument {
+    size_t size;
+    void* data;
+};
+
+static Array<u8, 32> arg_to_value_t(const Argument& arg)
+{
+    if (arg.size == 1)
+        return to_value_t(*(u8*)arg.data);
+
+    if (arg.size == 2)
+        return to_value_t(*(u16*)arg.data);
+
+    if (arg.size == 4)
+        return to_value_t(*(u32*)arg.data);
+
+    if (arg.size == 8)
+        return to_value_t(*(u64*)arg.data);
+
+    if (arg.size == 16) {
+        auto& data = *(charstar*)arg.data;
+        Array<unsigned char, 32> value { 0 };
+        for (size_t i = 0; i < 16; ++i)
+            value[i] = data[i];
+        return value;
+    }
+
+    if (arg.size == 32) {
+        auto& data = *(charstar*)arg.data;
+        auto length = strlen(data);
+        Array<unsigned char, 32> value { 0 };
+        for (size_t i = 0; i < length; ++i)
+            value[i] = data[i];
+        return value;
+    }
+
+    ASSERT_NOT_REACHED();
+}
+
+#define DECL_WITH_TYPE(ty)                          \
+    ty _##ty##arg0;                                 \
+    ty _##ty##arg1;                                 \
+    ty _##ty##arg2;                                 \
+    Argument ty##arg0 { sizeof(ty), &_##ty##arg0 }; \
+    Argument ty##arg1 { sizeof(ty), &_##ty##arg1 }; \
+    Argument ty##arg2 { sizeof(ty), &_##ty##arg2 };
+
+DECL_WITH_TYPE(int);
+DECL_WITH_TYPE(unsigned);
+DECL_WITH_TYPE(long);
+DECL_WITH_TYPE(longlong);
+DECL_WITH_TYPE(float);
+DECL_WITH_TYPE(double);
+DECL_WITH_TYPE(longdouble);
+
+#undef DECL_WITH_TYPE
+
+charstar _charstararg0;
+charstar _charstararg1;
+charstar _charstararg2;
+Argument charstararg0 { sizeof(charstar), &_charstararg0[0] };
+Argument charstararg1 { sizeof(charstar), &_charstararg1[0] };
+Argument charstararg2 { sizeof(charstar), &_charstararg2[0] };
+
+struct TestSuite {
+    const char* format;
+    const char* input;
+    int expected_output;
+    size_t argument_count;
+    Argument arguments[8];
+    Array<unsigned char, 32> expected_values[8]; // 32 bytes for each argument's value.
+};
+
+const TestSuite test_suites[] {
+    { "%d", "", 0, 0, {}, {} },
+    { "%x", "0x519", 1, 1, { unsignedarg0 }, { to_value_t(0x519) } },
+    { "%x", "0x51g", 1, 1, { unsignedarg0 }, { to_value_t(0x51u) } },
+    { "\"%%%d#", "\"%42#", 1, 1, { intarg0 }, { to_value_t(42) } },
+    { "  %d", "42", 1, 1, { intarg0 }, { to_value_t(42) } },
+    { "%d", "  42", 1, 1, { intarg0 }, { to_value_t(42) } },
+    { "%ld", "42", 1, 1, { longarg0 }, { to_value_t(42l) } },
+    { "%lld", "42", 1, 1, { longlongarg0 }, { to_value_t(42ll) } },
+    { "%f", "42", 1, 1, { floatarg0 }, { to_value_t(42.0f) } },
+    { "%lf", "42", 1, 1, { doublearg0 }, { to_value_t(42.0) } },
+    { "%s", "42", 1, 1, { charstararg0 }, { str_to_value_t("42") } },
+    { "%d%s", "42yoinks", 2, 2, { intarg0, charstararg0 }, { to_value_t(42), str_to_value_t("yoinks") } },
+    { "%[^\n]", "aaaa\n", 1, 1, { charstararg0 }, { str_to_value_t("aaaa") } },
+    { "%u.%u.%u", "3.19", 2, 3, { unsignedarg0, unsignedarg1, unsignedarg2 }, { to_value_t(3u), to_value_t(19u) } },
+    // Failing test case from previous impl:
+    { "SSH-%d.%d-%[^\n]\n", "SSH-2.0-OpenSSH_8.2p1 Ubuntu-4ubuntu0.1\n", 3, 3, { intarg0, intarg1, charstararg0 }, { to_value_t(2), to_value_t(0), str_to_value_t("OpenSSH_8.2p1 Ubuntu-4ubuntu0.1") } },
+};
+
+bool g_any_failed = false;
+
+static bool check_value_conformance(const TestSuite& test)
+{
+    bool fail = false;
+    for (int i = 0; i < test.expected_output; ++i) {
+        auto& arg = test.arguments[i];
+        auto arg_value = arg_to_value_t(arg);
+        auto& value = test.expected_values[i];
+        if (arg_value != value) {
+            auto arg_ptr = (const u32*)arg_value.data();
+            auto value_ptr = (const u32*)value.data();
+            printf("        value %d FAIL, expected %04x%04x%04x%04x%04x%04x%04x%04x but got %04x%04x%04x%04x%04x%04x%04x%04x\n",
+                i,
+                value_ptr[0], value_ptr[1], value_ptr[2], value_ptr[3],
+                value_ptr[4], value_ptr[5], value_ptr[6], value_ptr[7],
+                arg_ptr[0], arg_ptr[1], arg_ptr[2], arg_ptr[3],
+                arg_ptr[4], arg_ptr[5], arg_ptr[6], arg_ptr[7]);
+            fail = true;
+        } else {
+            printf("        value %d PASS\n", i);
+        }
+    }
+
+    return !fail;
+}
+
+static void do_one_test(const TestSuite& test)
+{
+    printf("Testing '%s' against '%s'...\n", test.input, test.format);
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wformat-nonliteral"
+    auto rc = sscanf(test.input, test.format,
+        test.arguments[0].data, test.arguments[1].data, test.arguments[2].data, test.arguments[3].data,
+        test.arguments[4].data, test.arguments[5].data, test.arguments[6].data, test.arguments[7].data);
+#pragma GCC diagnostic pop
+
+    bool overall = true;
+    printf("    output value...\n");
+    if (rc != test.expected_output) {
+        printf("    output value FAIL, expected %d but got %d\n", test.expected_output, rc);
+        overall = false;
+    } else {
+        printf("    output value PASS\n");
+    }
+
+    printf("    read values...\n");
+    if (check_value_conformance(test)) {
+        printf("    read values PASS\n");
+    } else {
+        printf("    read values FAIL\n");
+        overall = false;
+    }
+
+    if (overall)
+        printf("    overall PASS\n");
+    else
+        printf("    overall FAIL\n");
+
+    g_any_failed = g_any_failed || !overall;
+}
+
+int main()
+{
+    for (auto& test : test_suites)
+        do_one_test(test);
+
+    return g_any_failed ? 1 : 0;
+}