Nomad changes

docs/snippets/c/plugins/pdf_metadata_extractor.md

@@ -0,0 +1,85 @@
+```c title="C"
+#include <kreuzberg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/*
+ * The C FFI does not expose registration for custom DocumentExtractor
+ * implementations. To add PDF-specific behaviour from C, register a
+ * post-processor that runs only on PDF results and enriches them.
+ *
+ * The example below logs whenever the pipeline emits a PDF result, scoped
+ * via the should_process hook so it never fires for other MIME types.
+ */
+
+static char *dup_cstr(const char *s) {
+    size_t len = strlen(s);
+    char *out = (char *)malloc(len + 1);
+    if (out) {
+        memcpy(out, s, len + 1);
+    }
+    return out;
+}
+
+static int32_t process_fn(
+    const void *user_data,
+    const char *result,
+    const char *config,
+    char **out_error
+) {
+    (void)user_data;
+    (void)config;
+    (void)out_error;
+    printf("pdf-metadata-extractor: serialised PDF result is %zu bytes\n", strlen(result));
+    return 0;
+}
+
+static int32_t processing_stage_fn(
+    const void *user_data,
+    char **out_result
+) {
+    (void)user_data;
+    *out_result = dup_cstr("\"Late\"");
+    return 0;
+}
+
+static int32_t should_process_fn(
+    const void *user_data,
+    const char *result,
+    const char *config
+) {
+    (void)user_data;
+    (void)config;
+    return strstr(result, "\"mime_type\":\"application/pdf\"") != NULL;
+}
+
+static int32_t priority_fn(const void *user_data) {
+    (void)user_data;
+    return 75;
+}
+
+int main(void) {
+    KREUZBERGKreuzbergPostProcessorVTable vtable = {0};
+    vtable.process = process_fn;
+    vtable.processing_stage = processing_stage_fn;
+    vtable.should_process = should_process_fn;
+    vtable.priority = priority_fn;
+
+    char *err = NULL;
+    int32_t rc = kreuzberg_register_post_processor(
+        "pdf-metadata-extractor",
+        vtable,
+        NULL,
+        &err
+    );
+    if (rc != 0) {
+        fprintf(stderr, "register post-processor failed: %s\n", err ? err : "(no detail)");
+        kreuzberg_free_string(err);
+        return 1;
+    }
+
+    printf("pdf-metadata-extractor registered\n");
+    return 0;
+}
+```