[Debuginfod] Prune cache after fetch.

[mysterymath]

Summary

Previously, the size of the debuginfod cache would grow without bound.
This change prunes the cache after a successful debuginfod lookup, as is
done in libdebuginfod.

The cache pruning behavior is configured by a new
DEBUGINFOD_CACHE_POLICY environment variable. The semantics of this are
the same as --thinlto_cache_policy.

[gulfem]

Can you please add a test with DEBUGINFOD_CACHE_POLICY environment variable?

[mysterymath]

Add tests for caching behavior; fix timing issue.

[mysterymath]

Require curl in test.

llvm/lib/Debuginfod/Debuginfod.cpp

Expected<std::string> getCachedOrDownloadArtifact(
   HTTPClient Client;
   Client.setTimeout(Timeout);
   for (StringRef ServerUrl : DebuginfodUrls) {
     SmallString<64> ArtifactUrl;
     sys::path::append(ArtifactUrl, sys::path::Style::posix, ServerUrl, UrlPath);
 
     // Perform the HTTP request and if successful, write the response body to
     // the cache.
+    {
       StreamedHTTPResponseHandler Handler(
           [&]() { return CacheAddStream(Task, ""); }, Client);
       HTTPRequest Request(ArtifactUrl);
       Request.Headers = getHeaders();
       Error Err = Client.perform(Request, Handler);
       if (Err)
         return std::move(Err);
 
       unsigned Code = Client.responseCode();
       if (Code && Code != 200)
         continue;
+    }
+
+    Expected<CachePruningPolicy> PruningPolicyOrErr =
+        parseCachePruningPolicy(std::getenv("DEBUGINFOD_CACHE_POLICY"));
+    if (!PruningPolicyOrErr)
+      return PruningPolicyOrErr.takeError();
+    pruneCache(CacheDirectoryPath, *PruningPolicyOrErr);
 
     // Return the path to the artifact on disk.
     return std::string(AbsCachedArtifactPath);
   }
 
   return createStringError(errc::argument_out_of_domain, "build id not found");
 }
 

llvm/test/tools/llvm-debuginfod-find/cache.test

+REQUIRES: curl
+UNSUPPORTED: system-windows
+
+RUN: rm -rf %t/*
+RUN: mkdir -p %t/buildid/012345678901234{5,6}
+RUN: echo 'f' > %t/buildid/0123456789012345/debuginfo
+RUN: cp %t/buildid/012345678901234{5,6}/debuginfo
+RUN: mkdir %t/cache
+RUN: env DEBUGINFOD_CACHE_PATH=%t/cache DEBUGINFOD_URLS=file://%t \
+RUN:   llvm-debuginfod-find --debuginfo 0123456789012345 > /dev/null
+RUN: ls %t/cache | FileCheck --check-prefix=FIRST --match-full-lines --implicit-check-not {{.}} %s
+
+# Set policy to discard all but one file.
+RUN: env DEBUGINFOD_CACHE_POLICY=prune_interval=0s:cache_size_files=1 \
+RUN:     DEBUGINFOD_CACHE_PATH=%t/cache DEBUGINFOD_URLS=file://%t \
+RUN:     llvm-debuginfod-find --debuginfo 0123456789012346 > /dev/null
+RUN: ls %t/cache | FileCheck --check-prefix=SECOND --match-full-lines --implicit-check-not {{.}} %s
+
+# Add the first file back to the cache.
+RUN: env DEBUGINFOD_CACHE_PATH=%t/cache DEBUGINFOD_URLS=file://%t \
+RUN:     llvm-debuginfod-find --debuginfo 0123456789012345 > /dev/null
+RUN: ls %t/cache | FileCheck --check-prefix=BOTH --match-full-lines --implicit-check-not {{.}} %s
+
+# An invalid cache policy has no effect.
+RUN: env DEBUGINFOD_CACHE_POLICY=invalid:prune_interval=0s:cache_size_files=1 \
+RUN:     DEBUGINFOD_CACHE_PATH=%t/cache DEBUGINFOD_URLS=file://%t \
+RUN:     llvm-debuginfod-find --debuginfo 0123456789012346 > /dev/null
+RUN: ls %t/cache | FileCheck --check-prefix=BOTH --match-full-lines --implicit-check-not {{.}} %s
+
+FIRST: llvmcache-6663022027345102449
+FIRST: llvmcache.timestamp
+
+SECOND: llvmcache-6762748755046480574
+SECOND: llvmcache.timestamp
+
+BOTH: llvmcache-6663022027345102449
+BOTH: llvmcache-6762748755046480574
+BOTH: llvmcache.timestamp