feat: introduce streq and printErr

user/pipesink.c

@@ -0,0 +1,65 @@
+#include "ulib.h"
+
+/*
+ * Right half of shell.c's new `cmd1 | cmd2` pipeline syntax's live demo --
+ * see pipesrc.c's own header comment for the full picture. jobctlSpawnPiped
+ * bakes the SAME pipe's read end into this process's own fd 0 before it
+ * ever runs, so the blocking userRead below has to genuinely retry across
+ * timer ticks (fd 0's pipe end is flagged fdFlagBlocking, see
+ * vfsPipeAttachInto) until pipesrc.c's own write actually lands, exactly
+ * the same real cross-process wake this kernel's every other pipe/fifo
+ * demo already proves (schedWakeChannel via pipeWrite, pipe.c) -- never a
+ * coincidence of scheduling order (jobctlSpawnPiped installs pipesrc.c's
+ * write end into the pipe's writer count the moment IT is created, well
+ * before it ever runs, so this process can never see a false "no writer,
+ * EOF" even if it is scheduled to run first).
+ *
+ * Reads in a loop until a real EOF (0 return, once pipesrc.c has both
+ * written and exited -- see that file's own comment on why exit matters
+ * here) rather than trusting a single userRead call to receive the whole
+ * payload in one shot, the honest way a real pipe reader has to work.
+ *
+ * Unlike pipesrc.c, this process's own fd 1 (stdout) is NOT part of the
+ * pipeline (only fd 0 was redirected) -- print()/printDec() (ulib.h) reach
+ * the real console exactly like any unpiped demo, so the needle below is
+ * exactly as observable to ci-test.sh as every other one.
+ */
+
+static int streq(const char* a, const char* b)
+{
+    while (*a && *a == *b) {
+        a++;
+        b++;
+    }
+    return *a == *b;
+}
+
+int main(void)
+{
+    print("pipesink: blocking on read, waiting for pipesrc\n");
+
+    char buffer[64];
+    unsigned long total = 0;
+    for (;;) {
+        long got = userRead(0, buffer + total, sizeof(buffer) - 1 - total);
+        if (got < 0) {
+            print("pipesink: FAIL read\n");
+            return 1;
+        }
+        if (got == 0)
+            break;
+        total += (unsigned long)got;
+        if (total >= sizeof(buffer) - 1)
+            break;
+    }
+    buffer[total] = 0;
+
+    print("pipesink: got: ");
+    print(buffer);
+    print("\n");
+
+    int ok = streq(buffer, "pipeline-payload-ok");
+    print(ok ? "pipesink: payload-ok\n" : "pipesink: payload-FAIL\n");
+
+    return ok ? 0 : 1;
+}