1 files changed, 87 insertions, 1 deletions

diff --git a/py/stream.c b/py/stream.c
index 2b4410728f..4c8b8a570a 100644
--- a/py/stream.c
+++ b/py/stream.c
@@ -67,6 +67,9 @@ STATIC mp_obj_t stream_read(uint n_args, const mp_obj_t *args) {
         nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "Operation not supported"));
     }
 
+    // What to do if sz < -1?  Python docs don't specify this case.
+    // CPython does a readall, but here we silently let negatives through,
+    // and they will cause a MemoryError.
     mp_int_t sz;
     if (n_args == 1 || ((sz = mp_obj_get_int(args[1])) == -1)) {
         return stream_readall(args[0]);
@@ -74,7 +77,90 @@ STATIC mp_obj_t stream_read(uint n_args, const mp_obj_t *args) {
 
     #if MICROPY_PY_BUILTINS_STR_UNICODE
     if (!o->type->stream_p->is_bytes) {
-        mp_not_implemented("Reading from unicode text streams by character count");
+        // We need to read sz number of unicode characters.  Because we don't have any
+        // buffering, and because the stream API can only read bytes, we must read here
+        // in units of bytes and must never over read.  If we want sz chars, then reading
+        // sz bytes will never over-read, so we follow this approach, in a loop to keep
+        // reading until we have exactly enough chars.  This will be 1 read for text
+        // with ASCII-only chars, and about 2 reads for text with a couple of non-ASCII
+        // chars.  For text with lots of non-ASCII chars, it'll be pretty inefficient
+        // in time and memory.
+
+        vstr_t vstr;
+        vstr_init(&vstr, sz);
+        mp_uint_t more_bytes = sz;
+        mp_uint_t last_buf_offset = 0;
+        while (more_bytes > 0) {
+            char *p = vstr_add_len(&vstr, more_bytes);
+            if (p == NULL) {
+                nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_MemoryError, "out of memory"));
+            }
+            int error;
+            mp_int_t out_sz = o->type->stream_p->read(o, p, more_bytes, &error);
+            if (out_sz == -1) {
+                vstr_cut_tail_bytes(&vstr, more_bytes);
+                if (is_nonblocking_error(error)) {
+                    // With non-blocking streams, we read as much as we can.
+                    // If we read nothing, return None, just like read().
+                    // Otherwise, return data read so far.
+                    // TODO what if we have read only half a non-ASCII char?
+                    if (vstr.len == 0) {
+                        vstr_clear(&vstr);
+                        return mp_const_none;
+                    }
+                    break;
+                }
+                nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_OSError, "[Errno %d]", error));
+            }
+
+            if (out_sz == 0) {
+                // Finish reading.
+                // TODO what if we have read only half a non-ASCII char?
+                vstr_cut_tail_bytes(&vstr, more_bytes);
+                break;
+            }
+
+            // count chars from bytes just read
+            for (mp_uint_t off = last_buf_offset;;) {
+                byte b = vstr.buf[off];
+                int n;
+                if (!UTF8_IS_NONASCII(b)) {
+                    // 1-byte ASCII char
+                    n = 1;
+                } else if ((b & 0xe0) == 0xc0) {
+                    // 2-byte char
+                    n = 2;
+                } else if ((b & 0xf0) == 0xe0) {
+                    // 3-byte char
+                    n = 3;
+                } else if ((b & 0xf8) == 0xf0) {
+                    // 4-byte char
+                    n = 4;
+                } else {
+                    // TODO
+                    n = 5;
+                }
+                if (off + n <= vstr.len) {
+                    // got a whole char in n bytes
+                    off += n;
+                    sz -= 1;
+                    last_buf_offset = off;
+                    if (off >= vstr.len) {
+                        more_bytes = sz;
+                        break;
+                    }
+                } else {
+                    // didn't get a whole char, so work out how many extra bytes are needed for
+                    // this partial char, plus bytes for additional chars that we want
+                    more_bytes = (off + n - vstr.len) + (sz - 1);
+                    break;
+                }
+            }
+        }
+
+        mp_obj_t ret = mp_obj_new_str_of_type(&mp_type_str, (byte*)vstr.buf, vstr.len);
+        vstr_clear(&vstr);
+        return ret;
     }
     #endif