Independent Publisher 2: Don't Show Gravatar if it's the Default Gravatar

* Uses caching to help lessen queries.
* Code forked from https://gist.github.com/justinph/5197810

Closes #145

independent-publisher-2/header.php

@@ -28,7 +28,7 @@
 				<div class="site-branding">
 					<?php the_custom_logo(); ?>
 
-					<?php if ( '' !== get_theme_mod( 'independent_publisher_2_gravatar_email', get_option( 'admin_email' ) ) ) : ?>
+					<?php if ( '' !== get_theme_mod( 'independent_publisher_2_gravatar_email', get_option( 'admin_email' ) ) && validate_gravatar( get_theme_mod( 'independent_publisher_2_gravatar_email', get_option( 'admin_email' ) ) ) ) : ?>
 						<a class="site-logo-link" href="<?php echo esc_url( home_url( '/' ) ); ?>">
 							<img alt="" class="site-logo-image no-grav" width="80" height="80" src="<?php echo esc_url( get_avatar_url( get_theme_mod( 'independent_publisher_2_gravatar_email', get_option( 'admin_email' ) ), array( 'size' => 160 ) ) ); ?>" />
 						</a><!-- .site-logo-link -->

independent-publisher-2/inc/extras.php

@@ -67,3 +67,60 @@ function independent_publisher_2_pingback_header() {
 	}
 }
 add_action( 'wp_head', 'independent_publisher_2_pingback_header' );
+
+/**
+ * Utility function to check if a gravatar exists for a given email or id
+ * @param int|string|object $id_or_email A user ID,  email address, or comment object
+ * @return bool if the gravatar exists or not
+ * @link https://gist.github.com/justinph/5197810
+ */
+
+function validate_gravatar( $id_or_email ) {
+	// The id or email code is borrowed from wp-includes/pluggable.php.
+	$email = '';
+	if ( is_numeric( $id_or_email ) ) {
+		$id   = (int) $id_or_email;
+		$user = get_userdata( $id );
+		if ( $user ) {
+			$email = $user->user_email;
+		}
+	} elseif ( is_object( $id_or_email ) ) {
+		// No avatar for pingbacks or trackbacks.
+		$allowed_comment_types = apply_filters( 'get_avatar_comment_types', array( 'comment' ) );
+		if ( ! empty( $id_or_email->comment_type ) && ! in_array( $id_or_email->comment_type, (array) $allowed_comment_types, true ) ) {
+			return false;
+		}
+
+		if ( ! empty( $id_or_email->user_id ) ) {
+			$id   = (int) $id_or_email->user_id;
+			$user = get_userdata( $id );
+			if ( $user ) {
+				$email = $user->user_email;
+			}
+		} elseif ( ! empty( $id_or_email->comment_author_email ) ) {
+			$email = $id_or_email->comment_author_email;
+		}
+	} else {
+		$email = $id_or_email;
+	}
+
+	$hashkey = md5( strtolower( trim( $email ) ) );
+	$uri     = 'http://www.gravatar.com/avatar/' . $hashkey . '?d=404';
+	$data    = wp_cache_get( $hashkey );
+	$expire  = 60 * 5;
+	$group   = '';
+	if ( false === $data ) {
+		$response = wp_remote_head( $uri );
+		if ( is_wp_error( $response ) ) {
+			$data = 'not200';
+		} else {
+			$data = $response['response']['code'];
+		}
+		wp_cache_set( $hashkey, $data, $group, $expire );
+	}
+	if ( 200 === $data ) {
+		return true;
+	} else {
+		return false;
+	}
+}