Index: llvm/include/llvm/Debuginfod/Debuginfod.h
===================================================================
--- /dev/null
+++ llvm/include/llvm/Debuginfod/Debuginfod.h
@@ -0,0 +1,65 @@
+//===-- llvm/Debuginfod/Debuginfod.h - Debuginfod client --------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file contains the declarations of getCachedOrDownloadArtifact and
+/// several convenience functions for specific artifact types:
+/// getCachedOrDownloadSource, getCachedOrDownloadExecutable, and
+/// getCachedOrDownloadDebuginfo. This file also declares
+/// getDefaultDebuginfodUrls and getDefaultDebuginfodCacheDirectory.
+///
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_DEBUGINFOD_DEBUGINFOD_H
+#define LLVM_DEBUGINFOD_DEBUGINFOD_H
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/MemoryBuffer.h"
+
+namespace llvm {
+
+typedef ArrayRef<uint8_t> BuildID;
+
+// Finds default array of Debuginfod server URLs by checking DEBUGINFOD_URLS
+// environment variable.
+Expected<SmallVector<StringRef>> getDefaultDebuginfodUrls();
+
+// Finds a default local file caching directory for the debuginfod client.
+Expected<std::string> getDefaultDebuginfodCacheDirectory();
+
+// Fetches a specified source file by searching the default local cache
+// directory and server URLs.
+Expected<std::string> getCachedOrDownloadSource(BuildID ID,
+                                                StringRef SourceFilePath);
+
+// Fetches an executable by searching the default local cache directory and
+// server URLs.
+Expected<std::string> getCachedOrDownloadExecutable(BuildID ID);
+
+// Fetches a debug binary by searching the default local cache directory and
+// server URLs.
+Expected<std::string> getCachedOrDownloadDebuginfo(BuildID ID);
+
+// Fetches any debuginfod artifact using the default local cache directory and
+// server URLs.
+Expected<std::string> getCachedOrDownloadArtifact(StringRef UniqueKey,
+                                                  StringRef UrlPath);
+
+// Fetches any debuginfod artifact using the specified local cache directory and
+// server URLs. If the file is found, uses the UniqueKey for the local cache
+// file.
+Expected<std::string>
+getCachedOrDownloadArtifact(StringRef UniqueKey, StringRef UrlPath,
+                            StringRef CacheDirectoryPath,
+                            ArrayRef<StringRef> DebuginfodUrls);
+
+} // end namespace llvm
+
+#endif
Index: llvm/lib/CMakeLists.txt
===================================================================
--- llvm/lib/CMakeLists.txt
+++ llvm/lib/CMakeLists.txt
@@ -25,6 +25,7 @@
 add_subdirectory(ObjectYAML)
 add_subdirectory(Option)
 add_subdirectory(Remarks)
+add_subdirectory(Debuginfod)
 add_subdirectory(DebugInfo)
 add_subdirectory(DWP)
 add_subdirectory(ExecutionEngine)
Index: llvm/lib/Debuginfod/CMakeLists.txt
===================================================================
--- /dev/null
+++ llvm/lib/Debuginfod/CMakeLists.txt
@@ -0,0 +1,9 @@
+add_llvm_component_library(LLVMDebuginfod
+  Debuginfod.cpp
+
+  ADDITIONAL_HEADER_DIRS
+  ${LLVM_MAIN_INCLUDE_DIR}/llvm/Debuginfod
+
+  LINK_COMPONENTS
+  Support
+  )
Index: llvm/lib/Debuginfod/Debuginfod.cpp
===================================================================
--- /dev/null
+++ llvm/lib/Debuginfod/Debuginfod.cpp
@@ -0,0 +1,165 @@
+//===-- llvm/Debuginfod/Debuginfod.cpp - Debuginfod client library --------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+///
+/// This file defines the fetchInfo function, which retrieves
+/// any of the three supported artifact types: (executable, debuginfo, source
+/// file) associated with a build-id from debuginfod servers. If a source file
+/// is to be fetched, its absolute path must be specified in the Description
+/// argument to fetchInfo.
+///
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Debuginfod/Debuginfod.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/CachePruning.h"
+#include "llvm/Support/Caching.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/FileUtilities.h"
+#include "llvm/Support/HTTPClient.h"
+#include "llvm/Support/xxhash.h"
+
+using namespace llvm;
+
+static std::string uniqueKey(llvm::StringRef S) { return utostr(xxHash64(S)); }
+
+namespace llvm {
+// Returns a binary BuildID as a normalized hex string.
+// Uses lowercase for compatibility with common debuginfod servers.
+static std::string buildIDToString(BuildID ID) {
+  return llvm::toHex(ID, /*LowerCase=*/true);
+}
+
+Expected<SmallVector<StringRef>> getDefaultDebuginfodUrls() {
+  const char *DebuginfodUrlsEnv = std::getenv("DEBUGINFOD_URLS");
+  if (DebuginfodUrlsEnv == NULL)
+    return createStringError(errc::invalid_argument,
+                             "Missing DEBUGINFOD_URLS environment variable.");
+
+  SmallVector<StringRef> DebuginfodUrls;
+  StringRef(DebuginfodUrlsEnv).split(DebuginfodUrls, " ");
+  return DebuginfodUrls;
+}
+
+Expected<std::string> getDefaultDebuginfodCacheDirectory() {
+  SmallString<64> CacheDirectory;
+  if (!sys::path::cache_directory(CacheDirectory))
+    return createStringError(
+        errc::io_error, "Unable to determine appropriate cache directory.");
+  return std::string(CacheDirectory);
+}
+
+/// The following functions fetch a debuginfod artifact to a file in a local
+/// cache and return the cached file path. They first search the local cache,
+/// followed by the debuginfod servers.
+
+Expected<std::string> getCachedOrDownloadSource(BuildID ID,
+                                                StringRef SourceFilePath) {
+  SmallString<64> UrlPath;
+  // TODO: convert \ to / in SourceFilePath for compatibility with non-posix
+  // filesystems.
+  sys::path::append(UrlPath, sys::path::Style::posix, "buildid",
+                    buildIDToString(ID), "source", SourceFilePath);
+  return getCachedOrDownloadArtifact(uniqueKey(UrlPath), UrlPath);
+}
+
+Expected<std::string> getCachedOrDownloadExecutable(BuildID ID) {
+  SmallString<64> UrlPath;
+  sys::path::append(UrlPath, sys::path::Style::posix, "buildid",
+                    buildIDToString(ID), "executable");
+  return getCachedOrDownloadArtifact(uniqueKey(UrlPath), UrlPath);
+}
+
+Expected<std::string> getCachedOrDownloadDebuginfo(BuildID ID) {
+  SmallString<64> UrlPath;
+  sys::path::append(UrlPath, sys::path::Style::posix, "buildid",
+                    buildIDToString(ID), "debuginfo");
+  return getCachedOrDownloadArtifact(uniqueKey(UrlPath), UrlPath);
+}
+
+// General fetching function.
+Expected<std::string> getCachedOrDownloadArtifact(StringRef UniqueKey,
+                                                  StringRef UrlPath) {
+  Expected<std::string> CacheDirOrErr = getDefaultDebuginfodCacheDirectory();
+  if (Error Err = CacheDirOrErr.takeError())
+    return Err;
+  std::string &CacheDir = *CacheDirOrErr;
+  Expected<SmallVector<StringRef>> DebuginfodUrlsOrErr =
+      getDefaultDebuginfodUrls();
+  if (Error Err = DebuginfodUrlsOrErr.takeError())
+    return Err;
+  SmallVector<StringRef> &DebuginfodUrls = *DebuginfodUrlsOrErr;
+  return getCachedOrDownloadArtifact(UniqueKey, UrlPath, CacheDir,
+                                     DebuginfodUrls);
+}
+
+Expected<std::string>
+getCachedOrDownloadArtifact(StringRef UniqueKey, StringRef UrlPath,
+                            StringRef CacheDirectoryPath,
+                            ArrayRef<StringRef> DebuginfodUrls) {
+  SmallString<64> AbsCachedArtifactPath;
+  sys::path::append(AbsCachedArtifactPath, CacheDirectoryPath,
+                    "llvmcache-" + UniqueKey);
+
+  Expected<FileCache> CacheOrErr =
+      localCache("Debuginfod-client", ".debuginfod-client", CacheDirectoryPath,
+                 [](size_t Task, std::unique_ptr<MemoryBuffer> MB) {});
+  if (Error Err = CacheOrErr.takeError())
+    return Err;
+
+  FileCache Cache = *CacheOrErr;
+  // We choose an arbitrary Task parameter as we do not make use of it.
+  unsigned Task = 0;
+  Expected<AddStreamFn> CacheAddStreamOrErr = Cache(Task, UniqueKey);
+  if (Error Err = CacheAddStreamOrErr.takeError())
+    return Err;
+  AddStreamFn &CacheAddStream = *CacheAddStreamOrErr;
+  if (!CacheAddStream)
+    return std::string(AbsCachedArtifactPath);
+
+  // The artifact was not found in the local cache, query the debuginfod
+  // servers.
+  if (!HTTPClient::isAvailable())
+    return createStringError(errc::io_error,
+                             "No working HTTP client is available.");
+
+  for (const StringRef &ServerUrl : DebuginfodUrls) {
+    SmallString<64> ArtifactUrl;
+    sys::path::append(ArtifactUrl, sys::path::Style::posix, ServerUrl, UrlPath);
+
+    Expected<HTTPResponseBuffer> ResponseOrErr = HTTPClient().get(ArtifactUrl);
+    if (Error Err = ResponseOrErr.takeError())
+      return Err;
+
+    HTTPResponseBuffer &Response = *ResponseOrErr;
+    if (Response.Code != 200)
+      continue;
+
+    // We have retrieved the artifact from this server, and now add it to the
+    // file cache.
+    Expected<std::unique_ptr<CachedFileStream>> FileStreamOrErr =
+        CacheAddStream(Task);
+    if (Error Err = FileStreamOrErr.takeError())
+      return Err;
+    std::unique_ptr<CachedFileStream> &FileStream = *FileStreamOrErr;
+    if (!Response.Body)
+      return createStringError(
+          errc::io_error, "Unallocated MemoryBuffer in HTTPResponseBuffer.");
+
+    *FileStream->OS << StringRef(Response.Body->getBufferStart(),
+                                 Response.Body->getBufferSize());
+
+    // Return the path to the artifact on disk.
+    return std::string(AbsCachedArtifactPath);
+  }
+
+  return createStringError(errc::argument_out_of_domain, "build id not found");
+}
+
+} // namespace llvm
Index: llvm/unittests/CMakeLists.txt
===================================================================
--- llvm/unittests/CMakeLists.txt
+++ llvm/unittests/CMakeLists.txt
@@ -22,6 +22,7 @@
 add_subdirectory(Bitstream)
 add_subdirectory(CodeGen)
 add_subdirectory(DebugInfo)
+add_subdirectory(Debuginfod)
 add_subdirectory(Demangle)
 add_subdirectory(ExecutionEngine)
 add_subdirectory(FileCheck)
Index: llvm/unittests/Debuginfod/CMakeLists.txt
===================================================================
--- /dev/null
+++ llvm/unittests/Debuginfod/CMakeLists.txt
@@ -0,0 +1,9 @@
+set(LLVM_LINK_COMPONENTS
+  Debuginfod
+  )
+
+add_llvm_unittest(DebuginfodTests
+  DebuginfodTests.cpp
+  )
+
+target_link_libraries(DebuginfodTests PRIVATE LLVMTestingSupport)
Index: llvm/unittests/Debuginfod/DebuginfodTests.cpp
===================================================================
--- /dev/null
+++ llvm/unittests/Debuginfod/DebuginfodTests.cpp
@@ -0,0 +1,14 @@
+//===-- llvm/unittest/Support/DebuginfodTests.cpp - unit tests --*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Debuginfod/Debuginfod.h"
+#include "llvm/Testing/Support/Error.h"
+#include "gtest/gtest.h"
+
+/// TODO: test Debuginfod client functionality. This will be easier to test with
+/// either a working HTTP server or a refactor of the Debuginfod library.