Surface the real error when magic-mode flashing fails

bin/prod/flash-from-url

@@ -31,7 +31,38 @@ info "Overwriting block device $OUTFILE"
 info "Umounting /dev/mmcblk*"
 mount | grep '/dev/mmcblk' | cut -f 1 -d' ' | xargs -t -r -n 1 umount || true
 info "Starting flashing..."
-(wget -q -O - "$URL" | pv -f -n -b | xz -T 0 -d -c > "$OUTFILE") 2> /tmp/recore-flash-progress
+# pv's progress goes to /tmp/recore-flash-progress for the UI to poll - but
+# redirecting the whole pipeline's stderr there swallowed wget's and xz's
+# real error output too, leaving only "an unknown error" for the operator
+# (#59). Capture each stage's stderr separately instead, and report whichever
+# stage actually failed via PIPESTATUS.
+WGET_ERR="$(mktemp)"
+XZ_ERR="$(mktemp)"
+# -q also suppresses wget's error output, not just its progress noise -
+# needs to be silent on stdout (that's the actual image data) but not
+# on stderr, where the real error message would otherwise go missing.
+if wget -O - "$URL" 2>"$WGET_ERR" | pv -f -n -b 2> /tmp/recore-flash-progress | xz -T 0 -d -c 2>"$XZ_ERR" > "$OUTFILE"; then
+  PIPE_STATUS=("${PIPESTATUS[@]}")
+  PIPE_OK=1
+else
+  PIPE_STATUS=("${PIPESTATUS[@]}")
+  PIPE_OK=0
+fi
+
+if [ "$PIPE_OK" -eq 0 ]; then
+  if [ "${PIPE_STATUS[0]}" -ne 0 ]; then
+    # tail -1 would grab wget's trailing blank line rather than the actual
+    # "ERROR 404: Not Found." line before it - take the last non-empty line.
+    info "Download failed: $(awk 'NF{line=$0} END{print line}' "$WGET_ERR")"
+  elif [ "${PIPE_STATUS[2]}" -ne 0 ]; then
+    info "Decompression failed: $(awk 'NF{line=$0} END{print line}' "$XZ_ERR")"
+  else
+    info "Flashing pipeline failed (exit codes: ${PIPE_STATUS[*]})"
+  fi
+  rm -f "$WGET_ERR" "$XZ_ERR"
+  exit 1
+fi
+rm -f "$WGET_ERR" "$XZ_ERR"
 info "Flashing done"
 sync
 

reflash/server.go

@@ -770,7 +770,14 @@ func goMagic(url string) {
 	if err != nil {
 		logError("Error encountered during magic: \n" + stdout)
 		state.State = ERROR
-		state.Error = "An error was encountered during magic. Check log for details"
+		// flash-from-url prints the specific reason (e.g. the real download
+		// error, not just "an unknown error" - #59) as its last line before
+		// exiting non-zero. Surface that instead of a generic message.
+		state.Error = "An error was encountered during magic"
+		lines := strings.Split(strings.TrimSpace(stdout), "\n")
+		if lastLine := lines[len(lines)-1]; lastLine != "" {
+			state.Error = lastLine
+		}
 		return
 	}
 

test/bats/flash-from-url.bats

@@ -40,16 +40,12 @@ teardown() { teardown_sandbox; }
   [ "$status" -ne 0 ]
 }
 
-# Issue #59: the operator currently sees only "unknown error" because the
-# download pipeline's stderr is redirected into /tmp/recore-flash-progress
-# instead of being surfaced. Un-skip this once flash-from-url reports the real
-# cause on stdout/in the log.
-@test "flash-from-url: surfaces the real download error (#59 — pending fix)" {
-  skip "flash-from-url still redirects pipeline stderr to /tmp; un-skip when #59 is fixed"
-  stub wget 1 <<'ERR'
+@test "flash-from-url: surfaces the real download error (#59)" {
+  stub_stderr wget 1 <<'ERR'
 wget: unable to resolve host address 'example'
 ERR
   stub_silent xz 0
   run "$PROD_BIN/flash-from-url" http://example/image.img.xz
+  [ "$status" -ne 0 ]
   [[ "$output" == *"unable to resolve host"* ]]
 }

test/bats/helper.bash

@@ -47,6 +47,27 @@ stub() {
   chmod +x "$SHIMDIR/$name"
 }
 
+# stub_stderr NAME [EXIT_CODE]   (canned stderr read from this function's stdin)
+# Same as stub, but the heredoc body goes to stderr - for commands like wget
+# that write their real diagnostics there, not stdout.
+#
+#   stub_stderr wget 1 <<'ERR'
+#   wget: unable to resolve host address 'example'
+#   ERR
+stub_stderr() {
+  local name="$1" code="${2:-0}" body
+  body="$(cat)"
+  {
+    echo '#!/usr/bin/env bash'
+    echo "echo \"$name \$*\" >> \"$CALLS\""
+    echo "cat <<'__STUB_ERR__' >&2"
+    printf '%s\n' "$body"
+    echo '__STUB_ERR__'
+    echo "exit $code"
+  } > "$SHIMDIR/$name"
+  chmod +x "$SHIMDIR/$name"
+}
+
 # stub_silent NAME [EXIT_CODE] — a fake command with no stdout (records argv).
 # Handy for no-op system tools (mount, sleep, partprobe, ...) and for making a
 # command "fail" with a chosen exit code.