scpi_serial: Get rid of intermediate buffer, do not strip newline

Lowlevel access functions should not alter the data. sr_scpi_get_string(),
which is called by most highlevel access functions, strips newlines
in a central place, and is only fed with data which contains newlines
as a final terminator.
IEEE 488.2 definite length blocks may contain arbitrary data, thus the
payload up to the provided length should be passed unaltered.

Track if the last received character is a newline, which can be used
by sr_scpi_get_string() and its callers to determine if the response
is complete.

diff --git a/src/scpi/scpi_serial.c b/src/scpi/scpi_serial.c
index 02242ef66b5dc86d36502e6b352e9e6b5b1079b1..6811ad3688345ad81a5d93b81732d6ab5d761df1 100644 (file)
--- a/src/scpi/scpi_serial.c
+++ b/src/scpi/scpi_serial.c
@@ -28,13 +28,9 @@
 
 #define LOG_PREFIX "scpi_serial"
 
-#define BUFFER_SIZE 1024
-
 struct scpi_serial {
        struct sr_serial_dev_inst *serial;
-       char buffer[BUFFER_SIZE];
-       size_t count;
-       size_t read;
+       char got_newline;
 };
 
 static const struct {
@@ -97,8 +93,7 @@ static int scpi_serial_open(struct sr_scpi_dev_inst *scpi)
        if (serial_flush(serial) != SR_OK)
                return SR_ERR;
 
-       sscpi->count = 0;
-       sscpi->read = 0;
+       sscpi->got_newline = 0;
 
        return SR_OK;
 }
@@ -145,7 +140,8 @@ static int scpi_serial_send(void *priv, const char *command)
 
 static int scpi_serial_read_begin(void *priv)
 {
-       (void) priv;
+       struct scpi_serial *sscpi = priv;
+       sscpi->got_newline = 0;
 
        return SR_OK;
 }
@@ -153,56 +149,33 @@ static int scpi_serial_read_begin(void *priv)
 static int scpi_serial_read_data(void *priv, char *buf, int maxlen)
 {
        struct scpi_serial *sscpi = priv;
-       int len, ret;
-
-       len = BUFFER_SIZE - sscpi->count;
+       int ret;
 
-       /* Try to read new data into the buffer if there is space. */
-       if (len > 0) {
-               ret = serial_read_nonblocking(sscpi->serial, sscpi->buffer + sscpi->count,
-                               BUFFER_SIZE - sscpi->count);
+       /* Try to read new data into the buffer. */
+       ret = serial_read_nonblocking(sscpi->serial, buf, maxlen);
 
-               if (ret < 0)
-                       return ret;
+       if (ret < 0)
+               return ret;
 
-               sscpi->count += ret;
+       if (ret > 0) {
+               sr_spew("Read %d bytes into buffer.", ret);
 
-               if (ret > 0)
-                       sr_spew("Read %d bytes into buffer.", ret);
-       }
-
-       /* Return as many bytes as possible from buffer, excluding any trailing newline. */
-       if (sscpi->read < sscpi->count) {
-               len = sscpi->count - sscpi->read;
-               if (len > maxlen)
-                       len = maxlen;
-               if (sscpi->buffer[sscpi->read + len - 1] == '\n')
-                       len--;
-               sr_spew("Returning %d bytes from buffer.", len);
-               memcpy(buf, sscpi->buffer + sscpi->read, len);
-               sscpi->read += len;
-               if (sscpi->read == BUFFER_SIZE) {
-                       sr_spew("Resetting buffer.");
-                       sscpi->count = 0;
-                       sscpi->read = 0;
+               if (buf[ret - 1] == '\n') {
+                       sscpi->got_newline = 1;
+                       sr_spew("Received terminator");
+               } else {
+                       sscpi->got_newline = 0;
                }
-               return len;
        }
 
-       return 0;
+       return ret;
 }
 
 static int scpi_serial_read_complete(void *priv)
 {
        struct scpi_serial *sscpi = priv;
 
-       /* If the next character is a newline, discard it and report complete. */
-       if (sscpi->read < sscpi->count && sscpi->buffer[sscpi->read] == '\n') {
-               sscpi->read++;
-               return 1;
-       } else {
-               return 0;
-       }
+       return sscpi->got_newline;
 }
 
 static int scpi_serial_close(struct sr_scpi_dev_inst *scpi)