From 24fb4b7fea8692752d7a3934670ab5d89b218223 Mon Sep 17 00:00:00 2001
From: Gabriella Gonzalez <gabriel@arista.com>
Date: Thu, 30 Jun 2022 15:45:40 -0700
Subject: [PATCH] Add support for `/log/` API

---
 cbits/nix.cpp | 30 +++++++++++++++++++++++++++++-
 src/Main.hs   | 36 +++++++++++++++++++++++-------------
 src/Nix.hsc   | 15 +++++++++++++++
 3 files changed, 67 insertions(+), 14 deletions(-)

diff --git a/cbits/nix.cpp b/cbits/nix.cpp
index bb4dd58..654488d 100644
--- a/cbits/nix.cpp
+++ b/cbits/nix.cpp
@@ -1,6 +1,7 @@
 #include <cstddef>
 #include <cstdlib>
 #include <nix/store-api.hh>
+#include <nix/log-store.hh>
 #include "nix.hh"
 
 using namespace nix;
@@ -161,7 +162,8 @@ void signString
 void dumpPath(char const * const hashPart, struct string * const output) {
     ref<Store> store = getStore();
 
-    std::optional<StorePath> storePath= store->queryPathFromHashPart(hashPart);
+    std::optional<StorePath> storePath =
+        store->queryPathFromHashPart(hashPart);
 
     if (storePath.has_value()) {
         StringSink sink;
@@ -174,4 +176,30 @@ void dumpPath(char const * const hashPart, struct string * const output) {
     }
 }
 
+void dumpLog(char const * const hashPart, struct string * const output) {
+    ref<Store> store = getStore();
+
+    std::optional<StorePath> storePath =
+        store->queryPathFromHashPart(hashPart);
+
+    if (storePath.has_value()) {
+        auto subs = getDefaultSubstituters();
+
+        subs.push_front(store);
+
+        for (auto & sub : subs) {
+            LogStore * logStore = dynamic_cast<LogStore *>(&*sub);
+
+            std::optional<std::string> log = logStore->getBuildLog(storePath.value());
+
+            if (log.has_value()) {
+                copyString(log.value(), output);
+            } else {
+                *output = emptyString;
+            }
+        }
+    } else {
+        *output = emptyString;
+    }
+}
 }
diff --git a/src/Main.hs b/src/Main.hs
index 4b140da..2b5c0f2 100644
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -251,7 +251,7 @@ makeApplication ApplicationOptions{..} request respond = do
                     Nothing        -> noSuchPath
                     Just storePath -> return storePath
 
-                PathInfo{ narSize, narHash } <- liftIO (Nix.queryPathInfo storePath)
+                PathInfo{ narHash } <- liftIO (Nix.queryPathInfo storePath)
 
                 Monad.unless (all (narHash ==) maybeExpectedNarHash) do
                     let headers = [ ("Content-Type", "text/plain") ]
@@ -273,21 +273,31 @@ makeApplication ApplicationOptions{..} request respond = do
                     Nothing    -> noSuchPath
                     Just bytes -> return bytes
 
-                let contentLength =
-                        ( ByteString.Lazy.toStrict
-                        . Builder.toLazyByteString
-                        . Builder.word64Dec
-                        ) narSize
+                let lazyBytes = ByteString.Lazy.fromStrict bytes
 
-                let headers =
-                        [ ("Content-Type", "text/plain")
-                        , ("Content-Length", contentLength)
-                        ]
-
-                let builder = Builder.byteString bytes
+                let headers = [ ("Content-Type", "text/plain") ]
 
                 let response =
-                        Wai.responseBuilder Types.status200 headers builder
+                        Wai.responseLBS Types.status200 headers lazyBytes
+
+                done response
+
+            | Just suffix <- ByteString.stripPrefix "/log/" rawPath
+            , 32 <= ByteString.length suffix -> do
+                let hashPart = ByteString.take 32 suffix
+
+                maybeBytes <- liftIO (Nix.dumpLog hashPart)
+
+                bytes <- case maybeBytes of
+                    Nothing    -> noSuchPath
+                    Just bytes -> return bytes
+
+                let lazyBytes = ByteString.Lazy.fromStrict bytes
+
+                let headers = [ ("Content-Type", "text/plain") ]
+
+                let response =
+                        Wai.responseLBS Types.status200 headers lazyBytes
 
                 done response
 
diff --git a/src/Nix.hsc b/src/Nix.hsc
index 6adbbe3..94b7ddf 100644
--- a/src/Nix.hsc
+++ b/src/Nix.hsc
@@ -275,3 +275,18 @@ dumpPath hashPart = do
                 if data_ == Foreign.nullPtr
                     then return Nothing
                     else fmap Just (fromString_ string_)
+
+foreign import ccall "dumpLog" dumpLog_
+    :: CString -> Ptr String_ -> IO ()
+
+dumpLog :: ByteString -> IO (Maybe ByteString)
+dumpLog hashPart = do
+    ByteString.useAsCString hashPart \cHashPart -> do
+        Foreign.alloca \output -> do
+            let open = dumpLog_ cHashPart output
+            let close = freeString output
+            Exception.bracket_ open close do
+                string_@String_{ data_} <- peek output
+                if data_ == Foreign.nullPtr
+                    then return Nothing
+                    else fmap Just (fromString_ string_)