1 files changed, 263 insertions, 0 deletions
diff --git a/src/cepis-http.c b/src/cepis-http.c
new file mode 100644
index 0000000..10fa023
--- /dev/null
+++ b/src/cepis-http.c
@@ -0,0 +1,263 @@
+/*
+ * Transport primitives for the cep.is COBOL client.
+ *
+ * COBOL has no HTTP, and `curl_easy_setopt` is variadic, which a COBOL
+ * CALL cannot express portably. Everything variadic therefore lives here,
+ * behind four fixed-signature entry points that a COBOL CALL can reach:
+ *
+ *   cepis_http_get         one GET, no retrying -- the policy stays in COBOL
+ *   cepis_sleep_ms         the backoff wait
+ *   cepis_monotonic_ms     the clock CFG-TOTAL-TIMEOUT-MS is measured on
+ *   cepis_http_date_delta  the RFC 9110 HTTP-date form of Retry-After
+ *
+ * All scalar arguments are `int` or `long long` passed BY REFERENCE, which
+ * COBOL declares as PIC S9(9) COMP-5 and PIC S9(18) COMP-5. All string
+ * arguments in are NUL-terminated by the caller. All string arguments out
+ * are blank-filled to their capacity, so the COBOL field they land in is a
+ * normal space-padded PIC X.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <strings.h>
+#include <time.h>
+
+#include <curl/curl.h>
+
+#define CEPIS_OK_TRANSPORT 0
+#define CEPIS_ERR_TRANSPORT 1
+#define CEPIS_ERR_TOO_LARGE 2
+
+struct cepis_body {
+    char *buf;
+    long cap;
+    long len;
+    int overflow;
+};
+
+struct cepis_header {
+    char *buf;
+    long cap;
+    int seen;
+};
+
+static int cepis_curl_ready;
+
+static void cepis_blank(char *dst, long cap)
+{
+    if (dst && cap > 0) {
+        memset(dst, ' ', (size_t)cap);
+    }
+}
+
+static void cepis_put(char *dst, long cap, const char *src)
+{
+    size_t n;
+
+    cepis_blank(dst, cap);
+    if (!dst || cap <= 0 || !src) {
+        return;
+    }
+    n = strlen(src);
+    if (n > (size_t)cap) {
+        n = (size_t)cap;
+    }
+    memcpy(dst, src, n);
+}
+
+static size_t cepis_on_body(char *ptr, size_t size, size_t nmemb, void *userdata)
+{
+    struct cepis_body *sink = (struct cepis_body *)userdata;
+    size_t n = size * nmemb;
+
+    if (sink->len + (long)n > sink->cap) {
+        sink->overflow = 1;
+        return 0;
+    }
+    memcpy(sink->buf + sink->len, ptr, n);
+    sink->len += (long)n;
+    return n;
+}
+
+static size_t cepis_on_header(char *ptr, size_t size, size_t nmemb, void *userdata)
+{
+    struct cepis_header *hdr = (struct cepis_header *)userdata;
+    size_t n = size * nmemb;
+    static const char name[] = "retry-after:";
+    size_t name_len = sizeof(name) - 1;
+    size_t start, end, len;
+
+    if (hdr->seen || n <= name_len || strncasecmp(ptr, name, name_len) != 0) {
+        return n;
+    }
+    start = name_len;
+    end = n;
+    while (start < end && (ptr[start] == ' ' || ptr[start] == '\t')) {
+        start++;
+    }
+    while (end > start && (ptr[end - 1] == '\r' || ptr[end - 1] == '\n' ||
+                           ptr[end - 1] == ' ' || ptr[end - 1] == '\t')) {
+        end--;
+    }
+    len = end - start;
+    if (len > (size_t)hdr->cap) {
+        len = (size_t)hdr->cap;
+    }
+    memcpy(hdr->buf, ptr + start, len);
+    hdr->seen = 1;
+    return n;
+}
+
+/*
+ * Perform one GET. Returns 0 when the exchange completed (whatever the
+ * status), 1 when it never completed, 2 when the body did not fit.
+ */
+int cepis_http_get(const char *url,
+                   const char *user_agent,
+                   const int *timeout_ms,
+                   int *http_status,
+                   char *retry_after,
+                   const int *retry_after_cap,
+                   char *body,
+                   const int *body_cap,
+                   int *body_len,
+                   char *error_msg,
+                   const int *error_cap)
+{
+    CURL *curl;
+    CURLcode rc;
+    struct curl_slist *headers = NULL;
+    struct cepis_body sink;
+    struct cepis_header hdr;
+    char errbuf[CURL_ERROR_SIZE];
+    long status = 0;
+    int result = CEPIS_ERR_TRANSPORT;
+
+    *http_status = 0;
+    *body_len = 0;
+    cepis_blank(retry_after, *retry_after_cap);
+    cepis_blank(error_msg, *error_cap);
+
+    if (!cepis_curl_ready) {
+        if (curl_global_init(CURL_GLOBAL_DEFAULT) != CURLE_OK) {
+            cepis_put(error_msg, *error_cap, "curl_global_init failed");
+            return CEPIS_ERR_TRANSPORT;
+        }
+        cepis_curl_ready = 1;
+    }
+
+    curl = curl_easy_init();
+    if (!curl) {
+        cepis_put(error_msg, *error_cap, "curl_easy_init failed");
+        return CEPIS_ERR_TRANSPORT;
+    }
+
+    sink.buf = body;
+    sink.cap = *body_cap;
+    sink.len = 0;
+    sink.overflow = 0;
+
+    hdr.buf = retry_after;
+    hdr.cap = *retry_after_cap;
+    hdr.seen = 0;
+
+    errbuf[0] = '\0';
+
+    headers = curl_slist_append(headers,
+                                "Accept: application/json, text/csv;q=0.9, */*;q=0.1");
+    headers = curl_slist_append(headers, "Accept-Encoding: identity");
+
+    curl_easy_setopt(curl, CURLOPT_URL, url);
+    curl_easy_setopt(curl, CURLOPT_HTTPGET, 1L);
+    curl_easy_setopt(curl, CURLOPT_USERAGENT, user_agent);
+    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
+    curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);
+    curl_easy_setopt(curl, CURLOPT_MAXREDIRS, 5L);
+    curl_easy_setopt(curl, CURLOPT_NOSIGNAL, 1L);
+    curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT_MS, (long)*timeout_ms);
+    curl_easy_setopt(curl, CURLOPT_TIMEOUT_MS, (long)*timeout_ms);
+    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, cepis_on_body);
+    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &sink);
+    curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, cepis_on_header);
+    curl_easy_setopt(curl, CURLOPT_HEADERDATA, &hdr);
+    curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, errbuf);
+
+    rc = curl_easy_perform(curl);
+
+    if (rc == CURLE_OK) {
+        curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &status);
+        *http_status = (int)status;
+        *body_len = (int)sink.len;
+        result = CEPIS_OK_TRANSPORT;
+    } else if (sink.overflow) {
+        cepis_put(error_msg, *error_cap, "response body exceeds the client buffer");
+        result = CEPIS_ERR_TOO_LARGE;
+    } else {
+        cepis_put(error_msg, *error_cap,
+                  errbuf[0] ? errbuf : curl_easy_strerror(rc));
+        result = CEPIS_ERR_TRANSPORT;
+    }
+
+    curl_slist_free_all(headers);
+    curl_easy_cleanup(curl);
+    return result;
+}
+
+/* Sleep for the backoff. Negative and zero waits return at once. */
+void cepis_sleep_ms(const int *ms)
+{
+    struct timespec req;
+
+    if (*ms <= 0) {
+        return;
+    }
+    req.tv_sec = *ms / 1000;
+    req.tv_nsec = (long)(*ms % 1000) * 1000000L;
+    while (nanosleep(&req, &req) == -1) {
+        break;
+    }
+}
+
+/*
+ * Milliseconds off a monotonic clock. Wall time would let a clock step
+ * during an NTP correction shorten or extend CFG-TOTAL-TIMEOUT-MS.
+ */
+void cepis_monotonic_ms(long long *out)
+{
+    struct timespec now;
+
+    if (clock_gettime(CLOCK_MONOTONIC, &now) != 0) {
+        *out = 0;
+        return;
+    }
+    *out = (long long)now.tv_sec * 1000LL + (long long)(now.tv_nsec / 1000000L);
+}
+
+/*
+ * Seconds from now until an HTTP-date, the second form Retry-After may
+ * take. Returns 0 and sets *seconds when the date parses, 1 otherwise.
+ * The numeric form is handled in COBOL, where it belongs.
+ */
+int cepis_http_date_delta(const char *value, int *seconds)
+{
+    time_t target;
+    time_t now;
+    double delta;
+
+    *seconds = 0;
+    target = curl_getdate(value, NULL);
+    if (target == (time_t)-1) {
+        return 1;
+    }
+    now = time(NULL);
+    delta = difftime(target, now);
+    if (delta < 0) {
+        delta = 0;
+    }
+    if (delta > 2147483000.0) {
+        delta = 2147483000.0;
+    }
+    *seconds = (int)delta;
+    return 0;
+}