Lay Pure out as a core with the parts selected around it

The app model, the tree store and the HTTP host lived in
prototypes/connections among the earlier document runtime, the store was
known only by its format's name, and Vega compiled six Pure sources by path.
Now, as the README's principle has it:

  core/   runtime, flow and the app model (module*.c), with what the core
          asks of storage (state.h, store.h)
  store/  the tree store (PURETRE3, PUREREC1)
  serve/  pure-serve: HTTP host, outbound delivery, JSON in place
  cli/    pure-run, pure-edit-module

A top-level make builds libpure.a (app model and store, for hosts to link)
and the hosts; make check runs the store's and the app model's tests. The
earlier runtime still builds from prototypes/connections against core/ and
store/ (check, check-tree and check-core pass). Design 009 records the rule:
parts by role behind libraries; git repositories split by coupling, so the
store stays here while its contract moves with the core, and Vega stays apart.

1 files changed, 41 insertions, 0 deletions

diff --git a/core/flow.c b/core/flow.c
new file mode 100644
index 0000000..1070c70
--- /dev/null
+++ b/core/flow.c
@@ -0,0 +1,41 @@
+#include "flow.h"
+#include <assert.h>
+
+void pure_transfer_abort(PureTransfer *t) {
+    if (!t->active) return;
+    PureRelease release = t->release;
+    void *owner = t->owner;
+    *t = (PureTransfer){0};
+    if (release) release(owner);
+}
+
+static void advance(PureTransfer *t) {
+    while (t->active && t->part < 2 && t->offset == t->spans[t->part].size) {
+        t->part++;
+        t->offset = 0;
+    }
+    if (t->active && t->part == 2) pure_transfer_abort(t);
+}
+
+void pure_transfer_init(PureTransfer *t, PureSpan header, PureSpan body,
+                        void *owner, PureRelease release) {
+    assert(!t->active);
+    assert((!header.size || header.data) && (!body.size || body.data));
+    *t = (PureTransfer){.spans = {header, body}, .owner = owner,
+                       .release = release, .active = true};
+    advance(t);
+}
+
+PureSpan pure_transfer_next(const PureTransfer *t, size_t limit) {
+    if (!t->active) return (PureSpan){0};
+    PureSpan span = t->spans[t->part];
+    size_t remaining = span.size - t->offset;
+    return (PureSpan){span.data + t->offset, remaining < limit ? remaining : limit};
+}
+
+bool pure_transfer_consume(PureTransfer *t, size_t bytes) {
+    if (!t->active || bytes > t->spans[t->part].size - t->offset) return false;
+    t->offset += bytes;
+    advance(t);
+    return true;
+}