lib: avoid fallthrough cases in switch statements

Commit b5a434f7f0ee4d64857f8592eced5b9007d83620 inhibits the warning
on implicit fallthrough cases, since the current coding of indicating
fallthrough with comments is falling out of fashion with new compilers.
This attempts to make the issue smaller by rewriting fallthroughs to no
longer fallthrough, via either breaking the cases or turning switch
statements into if statements.

  lib/content_encoding.c: the fallthrough codepath is simply copied
    into the case as it's a single line.
  lib/http_ntlm.c: the fallthrough case skips a state in the state-
    machine and fast-forwards to NTLMSTATE_LAST. Do this before the
    switch statement instead to set up the states that we actually
    want.
  lib/http_proxy.c: the fallthrough is just falling into exiting the
    switch statement which can be done easily enough in the case.
  lib/mime.c: switch statement rewritten as if statement.
  lib/pop3.c: the fallthrough case skips to the next state in the
    statemachine, do this explicitly instead.
  lib/urlapi.c: switch statement rewritten as if statement.
  lib/vssh/wolfssh.c: the fallthrough cases fast-forwards the state
    machine, do this by running another iteration of the switch
    statement instead.
  lib/vtls/gtls.c: switch statement rewritten as if statement.
  lib/vtls/nss.c: the fallthrough codepath is simply copied into the
    case as it's a single line. Also twiddle a comment to not be
    inside a non-brace if statement.

Closes: #7322
See-also: #7295
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

9 files changed, 67 insertions, 65 deletions

diff --git a/lib/content_encoding.c b/lib/content_encoding.c
index a84ff543b..c03637a39 100644
--- a/lib/content_encoding.c
+++ b/lib/content_encoding.c
@@ -240,7 +240,8 @@ static CURLcode inflate_stream(struct Curl_easy *data,
         }
         zp->zlib_init = ZLIB_UNINIT;    /* inflateEnd() already called. */
       }
-      /* FALLTHROUGH */
+      result = exit_zlib(data, z, &zp->zlib_init, process_zlib_error(data, z));
+      break;
     default:
       result = exit_zlib(data, z, &zp->zlib_init, process_zlib_error(data, z));
       break;
diff --git a/lib/http_ntlm.c b/lib/http_ntlm.c
index 627a11c5a..a6526db9f 100644
--- a/lib/http_ntlm.c
+++ b/lib/http_ntlm.c
@@ -198,6 +198,12 @@ CURLcode Curl_output_ntlm(struct Curl_easy *data, bool proxy)
 #endif
 
   Curl_bufref_init(&ntlmmsg);
+
+  /* connection is already authenticated, don't send a header in future
+   * requests so go directly to NTLMSTATE_LAST */
+  if(*state == NTLMSTATE_TYPE3)
+    *state = NTLMSTATE_LAST;
+
   switch(*state) {
   case NTLMSTATE_TYPE1:
   default: /* for the weird cases we (re)start here */
@@ -246,11 +252,6 @@ CURLcode Curl_output_ntlm(struct Curl_easy *data, bool proxy)
     }
     break;
 
-  case NTLMSTATE_TYPE3:
-    /* connection is already authenticated,
-     * don't send a header in future requests */
-    *state = NTLMSTATE_LAST;
-    /* FALLTHROUGH */
   case NTLMSTATE_LAST:
     Curl_safefree(*allocuserpwd);
     authp->done = TRUE;
diff --git a/lib/http_proxy.c b/lib/http_proxy.c
index ef403d7f4..d2c2a8c2a 100644
--- a/lib/http_proxy.c
+++ b/lib/http_proxy.c
@@ -904,7 +904,8 @@ static CURLcode CONNECT(struct Curl_easy *data,
         h->write_waker = NULL;
       }
     }
-      /* FALLTHROUGH */
+    break;
+
     default:
       break;
     }
diff --git a/lib/mime.c b/lib/mime.c
index 0bf1b46a4..110b740ff 100644
--- a/lib/mime.c
+++ b/lib/mime.c
@@ -462,11 +462,13 @@ static size_t encoder_base64_read(char *buffer, size_t size, bool ateof,
       /* Buffered data size can only be 0, 1 or 2. */
       ptr[2] = ptr[3] = '=';
       i = 0;
-      switch(st->bufend - st->bufbeg) {
-      case 2:
-        i = (st->buf[st->bufbeg + 1] & 0xFF) << 8;
-        /* FALLTHROUGH */
-      case 1:
+
+      /* If there is buffered data */
+      if(st->bufend != st->bufbeg) {
+
+        if(st->bufend - st->bufbeg == 2)
+          i = (st->buf[st->bufbeg + 1] & 0xFF) << 8;
+
         i |= (st->buf[st->bufbeg] & 0xFF) << 16;
         ptr[0] = base64[(i >> 18) & 0x3F];
         ptr[1] = base64[(i >> 12) & 0x3F];
@@ -476,7 +478,6 @@ static size_t encoder_base64_read(char *buffer, size_t size, bool ateof,
         }
         cursize += 4;
         st->pos += 4;
-        break;
       }
     }
   }
diff --git a/lib/pop3.c b/lib/pop3.c
index d3f3de6d4..57296cf9b 100644
--- a/lib/pop3.c
+++ b/lib/pop3.c
@@ -1011,7 +1011,9 @@ static CURLcode pop3_statemachine(struct Curl_easy *data,
       break;
 
     case POP3_QUIT:
-      /* fallthrough, just stop! */
+      state(data, POP3_STOP);
+      break;
+
     default:
       /* internal error */
       state(data, POP3_STOP);
diff --git a/lib/urlapi.c b/lib/urlapi.c
index 59123ed57..367ddca79 100644
--- a/lib/urlapi.c
+++ b/lib/urlapi.c
@@ -157,23 +157,23 @@ static size_t strlen_url(const char *url, bool relative)
       continue;
     }
 
-    switch(*ptr) {
-    case '?':
-      left = FALSE;
-      /* FALLTHROUGH */
-    default:
-      if(urlchar_needs_escaping(*ptr))
-        newlen += 2;
-      newlen++;
-      break;
-    case ' ':
+    if(*ptr == ' ') {
       if(left)
         newlen += 3;
       else
         newlen++;
-      break;
+      continue;
     }
+
+    if (*ptr == '?')
+      left = FALSE;
+
+    if(urlchar_needs_escaping(*ptr))
+      newlen += 2;
+
+    newlen++;
   }
+
   return newlen;
 }
 
@@ -202,19 +202,7 @@ static void strcpy_url(char *output, const char *url, bool relative)
       continue;
     }
 
-    switch(*iptr) {
-    case '?':
-      left = FALSE;
-      /* FALLTHROUGH */
-    default:
-      if(urlchar_needs_escaping(*iptr)) {
-        msnprintf(optr, 4, "%%%02x", *iptr);
-        optr += 3;
-      }
-      else
-        *optr++=*iptr;
-      break;
-    case ' ':
+    if(*iptr == ' ') {
       if(left) {
         *optr++='%'; /* add a '%' */
         *optr++='2'; /* add a '2' */
@@ -222,8 +210,18 @@ static void strcpy_url(char *output, const char *url, bool relative)
       }
       else
         *optr++='+'; /* add a '+' here */
-      break;
+      continue;
     }
+
+    if(*iptr == '?')
+      left = FALSE;
+
+    if(urlchar_needs_escaping(*iptr)) {
+      msnprintf(optr, 4, "%%%02x", *iptr);
+      optr += 3;
+    }
+    else
+      *optr++ = *iptr;
   }
   *optr = 0; /* null-terminate output buffer */
 
diff --git a/lib/vssh/wolfssh.c b/lib/vssh/wolfssh.c
index 4b1e2ec5e..5b4cde91b 100644
--- a/lib/vssh/wolfssh.c
+++ b/lib/vssh/wolfssh.c
@@ -449,7 +449,8 @@ static CURLcode wssh_statemach_act(struct Curl_easy *data, bool *block)
     switch(sshc->state) {
     case SSH_INIT:
       state(data, SSH_S_STARTUP);
-      /* FALLTHROUGH */
+      break;
+
     case SSH_S_STARTUP:
       rc = wolfSSH_connect(sshc->ssh_session);
       if(rc != WS_SUCCESS)
@@ -838,7 +839,8 @@ static CURLcode wssh_statemach_act(struct Curl_easy *data, bool *block)
         break;
       }
       state(data, SSH_SFTP_READDIR);
-      /* FALLTHROUGH */
+      break;
+
     case SSH_SFTP_READDIR:
       name = wolfSSH_SFTP_LS(sshc->ssh_session, sftp_scp->path);
       if(!name)
diff --git a/lib/vtls/gtls.c b/lib/vtls/gtls.c
index f3a308fbc..2053fd439 100644
--- a/lib/vtls/gtls.c
+++ b/lib/vtls/gtls.c
@@ -404,6 +404,7 @@ gtls_connect_step1(struct Curl_easy *data,
   const char * const hostname = SSL_HOST_NAME();
   long * const certverifyresult = &SSL_SET_OPTION_LVALUE(certverifyresult);
   const char *tls13support;
+  CURLcode result;
 
   if(connssl->state == ssl_connection_complete)
     /* to make us tolerant against being called more than once for the
@@ -557,31 +558,25 @@ gtls_connect_step1(struct Curl_easy *data,
   /* Ensure +SRP comes at the *end* of all relevant strings so that it can be
    * removed if a run-time error indicates that SRP is not supported by this
    * GnuTLS version */
-  switch(SSL_CONN_CONFIG(version)) {
-    case CURL_SSLVERSION_TLSv1_3:
-      if(!tls13support) {
-        failf(data, "This GnuTLS installation does not support TLS 1.3");
-        return CURLE_SSL_CONNECT_ERROR;
-      }
-      /* FALLTHROUGH */
-    case CURL_SSLVERSION_DEFAULT:
-    case CURL_SSLVERSION_TLSv1:
-    case CURL_SSLVERSION_TLSv1_0:
-    case CURL_SSLVERSION_TLSv1_1:
-    case CURL_SSLVERSION_TLSv1_2: {
-      CURLcode result = set_ssl_version_min_max(data, &prioritylist,
-                                                tls13support);
-      if(result)
-        return result;
-      break;
-    }
-    case CURL_SSLVERSION_SSLv2:
-    case CURL_SSLVERSION_SSLv3:
-    default:
-      failf(data, "GnuTLS does not support SSLv2 or SSLv3");
+
+  if(SSL_CONN_CONFIG(version) == CURL_SSLVERSION_SSLv2 ||
+     SSL_CONN_CONFIG(version) == CURL_SSLVERSION_SSLv3) {
+    failf(data, "GnuTLS does not support SSLv2 or SSLv3");
+    return CURLE_SSL_CONNECT_ERROR;
+  }
+
+  if(SSL_CONN_CONFIG(version) == CURL_SSLVERSION_TLSv1_3) {
+    if(!tls13support) {
+      failf(data, "This GnuTLS installation does not support TLS 1.3");
       return CURLE_SSL_CONNECT_ERROR;
+    }
   }
 
+  /* At this point we know we have a supported TLS version, so set it */
+  result = set_ssl_version_min_max(data, &prioritylist, tls13support);
+  if(result)
+    return result;
+
 #ifdef HAVE_GNUTLS_SRP
   /* Only add SRP to the cipher list if SRP is requested. Otherwise
    * GnuTLS will disable TLS 1.3 support. */
diff --git a/lib/vtls/nss.c b/lib/vtls/nss.c
index cf657895f..c9cc2fd09 100644
--- a/lib/vtls/nss.c
+++ b/lib/vtls/nss.c
@@ -2250,10 +2250,11 @@ static CURLcode nss_connect_common(struct Curl_easy *data,
   case CURLE_OK:
     break;
   case CURLE_AGAIN:
+    /* CURLE_AGAIN in non-blocking mode is not an error */
     if(!blocking)
-      /* CURLE_AGAIN in non-blocking mode is not an error */
       return CURLE_OK;
-    /* FALLTHROUGH */
+    else
+      return result;
   default:
     return result;
   }