From f9f27de91c89d826c6a39c3ef44fb1b02f9a43aa Mon Sep 17 00:00:00 2001
From: Elliot Gorokhovsky <embg@fb.com>
Date: Fri, 29 Jul 2022 14:44:22 -0700
Subject: [PATCH] Disallow empty output directory

---
 programs/zstdcli.c                             | 18 ++++++++++++++++--
 tests/cli-tests/basic/output_dir.sh            |  7 +++++++
 .../cli-tests/basic/output_dir.sh.stderr.exact |  2 ++
 .../cli-tests/basic/output_dir.sh.stdout.exact |  2 ++
 4 files changed, 27 insertions(+), 2 deletions(-)
 create mode 100755 tests/cli-tests/basic/output_dir.sh
 create mode 100644 tests/cli-tests/basic/output_dir.sh.stderr.exact
 create mode 100644 tests/cli-tests/basic/output_dir.sh.stdout.exact

diff --git a/programs/zstdcli.c b/programs/zstdcli.c
index fbacb908a..1143ac3fe 100644
--- a/programs/zstdcli.c
+++ b/programs/zstdcli.c
@@ -1011,7 +1011,14 @@ int main(int argCount, const char* argv[])
                 if (longCommandWArg(&argument, "--stream-size=")) { streamSrcSize = readSizeTFromChar(&argument); continue; }
                 if (longCommandWArg(&argument, "--target-compressed-block-size=")) { targetCBlockSize = readSizeTFromChar(&argument); continue; }
                 if (longCommandWArg(&argument, "--size-hint=")) { srcSizeHint = readSizeTFromChar(&argument); continue; }
-                if (longCommandWArg(&argument, "--output-dir-flat")) { NEXT_FIELD(outDirName); continue; }
+                if (longCommandWArg(&argument, "--output-dir-flat")) {
+                    NEXT_FIELD(outDirName);
+                    if (strlen(outDirName) == 0) {
+                        DISPLAY("error: output dir cannot be empty string (did you mean to pass '.' instead?)\n");
+                        CLEAN_RETURN(1);
+                    }
+                    continue;
+                }
                 if (longCommandWArg(&argument, "--auto-threads")) {
                     const char* threadDefault = NULL;
                     NEXT_FIELD(threadDefault);
@@ -1020,7 +1027,14 @@ int main(int argCount, const char* argv[])
                     continue;
                 }
 #ifdef UTIL_HAS_MIRRORFILELIST
-                if (longCommandWArg(&argument, "--output-dir-mirror")) { NEXT_FIELD(outMirroredDirName); continue; }
+                if (longCommandWArg(&argument, "--output-dir-mirror")) {
+                    NEXT_FIELD(outMirroredDirName);
+                    if (strlen(outMirroredDirName) == 0) {
+                        DISPLAY("error: output dir cannot be empty string (did you mean to pass '.' instead?)\n");
+                        CLEAN_RETURN(1);
+                    }
+                    continue;
+                }
 #endif
 #ifndef ZSTD_NOTRACE
                 if (longCommandWArg(&argument, "--trace")) { char const* traceFile; NEXT_FIELD(traceFile); TRACE_enable(traceFile); continue; }
diff --git a/tests/cli-tests/basic/output_dir.sh b/tests/cli-tests/basic/output_dir.sh
new file mode 100755
index 000000000..a8819d292
--- /dev/null
+++ b/tests/cli-tests/basic/output_dir.sh
@@ -0,0 +1,7 @@
+#!/bin/sh
+
+println "+ zstd -r * --output-dir-mirror=\"\""
+zstd -r * --output-dir-mirror="" && die "Should not allow empty output dir!"
+println "+ zstd -r * --output-dir-flat=\"\""
+zstd -r * --output-dir-flat="" && die "Should not allow empty output dir!"
+exit 0
diff --git a/tests/cli-tests/basic/output_dir.sh.stderr.exact b/tests/cli-tests/basic/output_dir.sh.stderr.exact
new file mode 100644
index 000000000..e12b50427
--- /dev/null
+++ b/tests/cli-tests/basic/output_dir.sh.stderr.exact
@@ -0,0 +1,2 @@
+error: output dir cannot be empty string (did you mean to pass '.' instead?)
+error: output dir cannot be empty string (did you mean to pass '.' instead?)
diff --git a/tests/cli-tests/basic/output_dir.sh.stdout.exact b/tests/cli-tests/basic/output_dir.sh.stdout.exact
new file mode 100644
index 000000000..1e478cd75
--- /dev/null
+++ b/tests/cli-tests/basic/output_dir.sh.stdout.exact
@@ -0,0 +1,2 @@
++ zstd -r * --output-dir-mirror=""
++ zstd -r * --output-dir-flat=""