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My site requires the use of https for all img src HTML.

This is the WordPress function I'm using to display images:

<img src="'.get_bloginfo("template_url").'/images/thumb-default.gif" />

This outputs an http img src - how can I convert that to https?

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4 Answers 4

up vote 8 down vote accepted

WordPress checks the return value of is_ssl() before creating URLs using get_bloginfo(). If the function returns true, it creates https URLs. If it returns false, it creates http URLs.

From the WordPress source ...

function is_ssl() {
    if ( isset($_SERVER['HTTPS']) ) {
        if ( 'on' == strtolower($_SERVER['HTTPS']) )
            return true;
        if ( '1' == $_SERVER['HTTPS'] )
            return true;
    } elseif ( isset($_SERVER['SERVER_PORT']) && ( '443' == $_SERVER['SERVER_PORT'] ) ) {
        return true;
    return false;

So ... if the request was made over https or if the request came in over port 443, then get_bloginfo() will return an https:// URL. In reality, if you're forcing https anyway, you should force all requests to port 80 (http) over to port 443 (https) ... but that's a server configuration issue, not a WordPress issue.

Alternatively, you could hook into a filter and replace http with https ...

Just use:

function replace_http( $original ) {
    // use preg_replace() to replace http:// with https://
    $output = preg_replace( "^http:", "https:", $original );
    return $output;

add_filter( 'template_url', 'replace_http' );
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I get a parse error when I add that code to my functions.php file. The $ouput line is also marked red in Dreamweaver. – Ryan Apr 18 '11 at 18:16
I didn't give you the full code ... you have to actually put something inside the preg_replace() code, and I can't give you the regex at the moment. Replace preg_replace( ... ); with the actual call and you should be fine. – EAMann Apr 18 '11 at 18:20
I'm not sure what to write. If you have time to provide the regex/full code I would greatly appreciate it! – Ryan Apr 18 '11 at 18:22
Updated with regex code. – EAMann Apr 18 '11 at 18:30
This solution only fixes links generated by code. What about insecure links/images added in to pages/posts using the editor? Is there a way to do a global preg replace on all of the output? – Phil_1984_ Aug 31 at 10:06

Had you checked this when requesting page via http or https link? What does is_ssl() return for you?

I don't have SSL-capable stack to test at moment, but I am pretty sure that WP functions that put together links should be aware of SSL and output correct version.

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The page URL in my browser is https, but the img src links are http. – Ryan Apr 18 '11 at 18:11
@Ryan this is not normal behavior, I've checked and it should be https link generated in such case... see EAMann's answer for extended details. – Rarst Apr 18 '11 at 18:13

Using the home_url() function will automatically detect ssl and change protocols.

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To add to the fix proposed by EAMann I have made some changes for version 3.5:

add_filter( 'template_directory_uri', function( $original ) {
    $output = preg_replace( "/^http:/i", "https:", $original );
    return $output;

I'd like to note that this redirect thing may be very helpful, but my server redirects SSL to another port and is not detected by WP so for me it's an annoyance.

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Are you referring to WordPress 3.5? Is so, that's great! – Ryan Apr 17 '13 at 17:23

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