apache - Multiple RewriteConditions: How to chain them before a set of rules?

Question

Q1: How to chain these two conditions making them if BOTH A AND B, then proceed...
Q2: How to make them stick for all the rewriteRules below and not just the first rule?

RewriteCond %{REQUEST_URI} ^IMAGE-.*$      // if filename starts with IMG- and,
RewriteCond %{REQUEST_FILENAME} !-f        // if file does exist, then proceed:
RewriteRule Rule1
RewriteRule Rule2
RewriteRule Rule3

# -- END IF -- STOP HERE -- #

Answer 1

Here are some tricks for making a RewriteCond stack apply to multiple RewriteRule's, sorted by increasing WTF's per minute. But this is configuration and not code, so those rules don't apply, right? :-)

1. Environment variable

When you have many RewriteCond's, storing their result in an environment variable and then testing against in every rule is more compact.

# Your RewriteCond stack.
RewriteCond %{REQUEST_URI} !^IMAGE-.*$ [OR]
RewriteCond %{REQUEST_FILENAME} -f
# Store environment variable.
RewriteRule ^ - [E=TRUE:YEP]
# Assert environment variable in remaining RewriteRule's.
RewriteCond %{ENV:TRUE} =YEP
RewriteRule Rule1
RewriteCond %{ENV:TRUE} =YEP
RewriteRule Rule2
RewriteCond %{ENV:TRUE} =YEP
RewriteRule Rule3

2. Skip flag

This one's a bit subtle. Using the [S] or [skip] flag you can cause your entire block of RewriteRule's to be skipped.

# Your RewriteCond stack.
RewriteCond %{REQUEST_URI} !^IMAGE-.*$ [OR]
RewriteCond %{REQUEST_FILENAME} -f
# If RewriteCond's match, skip the next RewriteRule.
RewriteRule ^ - [skip=1]
# Otherwise, this rule will match and the rest will be skipped.
RewriteRule ^ - [skip=3]
RewriteRule Rule1
RewriteRule Rule2
RewriteRule Rule3

This acts sort of like an if-statement with the RewriteCond's being the condition and RewriteRule's being the code block.

You get less duplication, but the tradeoff is the code is less clear, and you have to update [skip=N] every time you add or remove a rule from this set of N RewriteRule's.

<fun>

All right, if you're still reading, here you'll find two more solutions where the WTF's per minute reach and exceed a critical point. They're for amusement only, and you'll see why.

3. Skip flag without N

Yes, there is a way to use the [skip] flag without including N, the number of RewriteRule's you want to apply the RewriteCond stack to. That is... if you include a pair of RewriteCond's before each RewriteRule, and oh yeah, one more at the end.

# Your RewriteCond stack.
RewriteCond %{REQUEST_URI} !^IMAGE-.*$ [OR]
RewriteCond %{REQUEST_FILENAME} -f
# If RewriteCond's match, skip the next RewriteRule.
RewriteRule ^ - [skip=1]  # succeeded
RewriteRule ^ - [skip=2]  # failed
RewriteRule Rule1
RewriteRule ^ - [skip=1]  # succeeded
RewriteRule ^ - [skip=2]  # failed
RewriteRule Rule2
RewriteRule ^ - [skip=1]  # succeeded
RewriteRule ^ - [skip=2]  # failed
RewriteRule Rule3
RewriteRule ^ -           # no-op to cover for last [skip=2] rule

The trick here is that every [skip=1] rule gets processed if and only if the RewriteCond's succeeded, and every [skip=2] rule gets processed if and only if they failed.

4. URL marker

Use part of the URL to hold state then match against it in your RewriteRule's.

# Your RewriteCond stack.
RewriteCond %{REQUEST_URI} !^IMAGE-.*$ [OR]
RewriteCond %{REQUEST_FILENAME} -f
# If RewriteCond's match, prepend bogus marker "M#" to internal URL.
RewriteRule .* M#$0
# All your RewriteRule's test for this marker plus whatever else.
RewriteRule ^M#.*Rule1
RewriteRule ^M#.*Rule2
RewriteRule ^M#.*Rule3
# Finally, don't forget to strip off the bogus marker.
RewriteRule ^M#(.*) $1

The new URL with the marker is invalid, but the last RewriteRule revert it, right? Well, only if it gets processed, so don't let the marker URL escape this round of mod_rewrite processing before it gets reverted. You'll get a 404 then.