oss-fuzz-build: support branch switching

README-maintainer

@@ -25,6 +25,9 @@ GOOGLE OSS-FUZZ
 
 Clone the oss-fuzz project. From the root directory of the repository:
 
+  Add `-e GITHUB_FORK=fork -e GITHUB_BRANCH=branch` to build_fuzzers
+  to work off a fork/branch rather than qpdf/master.
+
   python infra/helper.py build_image --pull qpdf
   python infra/helper.py build_fuzzers qpdf
   python infra/helper.py check_build qpdf

fuzz/oss-fuzz-build

@@ -1,4 +1,4 @@
-#!/bin/bash -e
+#!/bin/bash -ex
 
 # This is used invoked from
 # https://github.com/google/oss-fuzz/blob/master/projects/qpdf/build.sh
@@ -6,6 +6,21 @@
 # It should be run from the top level directory of a clean checkout of
 # qpdf. It is also exercised in ../azure-pipelines/build-fuzzer
 
+if [[ $GITHUB_FORK != "" ]]; then
+    git remote add fork https://github.com/$GITHUB_FORK/qpdf
+    git fetch fork --depth=1
+    CUR_BRANCH=$(git rev-parse --abbrev-ref @)
+    if [[ $GITHUB_BRANCH == "" ]]; then
+        GITHUB_BRANCH=$CUR_BRANCH
+    fi
+    if [[ $GITHUB_BRANCH == $CUR_BRANCH ]]; then
+        git reset --hard fork/$CUR_BRANCH
+    else
+        git branch -f $GITHUB_BRANCH fork/$GITHUB_BRANCH
+        git checkout $GITHUB_BRANCH
+    fi
+fi
+
 ./configure \
   --enable-oss-fuzz \
   --enable-static \