[edit] Add line-editing library, libedit

Now used by the 6s shell to enable backspace, return, etc. No cursor
movement yet or anything complex.

src/libraries/edit/line.cpp

@@ -0,0 +1,137 @@
+#include <edit/line.h>
+#include <j6/memutils.h>
+#include <j6/syslog.hh>
+
+namespace edit {
+
+static constexpr char ESC = '\x1b';
+static constexpr char BACKSPACE = '\x08';
+static constexpr char DEL = '\x7f';
+
+static const char init_line[] = "\x1b[999D\x1b[K";
+static const size_t init_line_len = sizeof(init_line) - 1;
+
+static const char get_pos[] = "\x1b[n";
+static const size_t get_pos_len = sizeof(get_pos) - 1;
+
+static const char backspace[] = "\x1b[D\x1b[K";
+static const size_t backspace_len = sizeof(backspace) - 1;
+
+line::line(const char *prompt, size_t prompt_len) :
+    m_out {0}
+{
+    m_buf = new char [1024];
+    memcpy(m_buf, init_line, init_line_len);
+    m_in = init_line_len;
+
+    if (prompt && prompt_len) {
+        memcpy(m_buf + m_in, prompt, prompt_len);
+        m_in += prompt_len;
+    }
+
+    m_prefix = m_in;
+
+    m_tmp_out = get_pos;
+    m_tmp_out_len = get_pos_len;
+}
+
+
+line::~line()
+{
+    delete [] m_buf;
+}
+
+
+size_t
+line::input(char const *data, size_t len)
+{
+    j6::syslog(j6::logs::app, j6::log_level::spam, "Line edit got %d bytes input", len);
+    size_t i = 0;
+    size_t sub_len = 0;
+    while (i < len) {
+        switch (data[i]) {
+        case ESC:
+            sub_len = parse_command(data + i, len - i);
+            if (!sub_len)
+                return i; // Not yet enough data
+            i += sub_len;
+            break;
+
+        case BACKSPACE:
+        case DEL:
+            if (m_in > m_prefix) {
+                --m_in;
+                if (m_out > m_in)
+                    m_out = m_in;
+                m_tmp_out = backspace;
+                m_tmp_out_len = backspace_len;
+            }
+            ++i;
+            break;
+
+        case '\r':
+            m_out = 0;
+            m_in = m_prefix;
+            m_tmp_out = "\n";
+            m_tmp_out_len = 1;
+            ++i;
+            break;
+
+        default:
+            m_buf[m_in++] = data[i++];
+            break;
+        }
+    }
+
+    return i;
+}
+
+
+size_t
+line::output(char const **data)
+{
+    if (m_tmp_out) {
+        char const *out = m_tmp_out;
+        m_tmp_out = nullptr;
+
+        size_t len = m_tmp_out_len;
+        m_tmp_out_len = 0;
+
+        *data = out;
+        j6::syslog(j6::logs::app, j6::log_level::spam, "Line edit sending %d bytes alt output", len);
+        return len;
+    }
+
+    *data = (m_buf + m_out);
+    size_t len = m_in - m_out;
+    m_out = m_in;
+    j6::syslog(j6::logs::app, j6::log_level::spam, "Line edit sending %d bytes output", len);
+    return len;
+}
+
+
+size_t
+line::parse_command(char const *data, size_t len)
+{
+    size_t i = 2;
+
+    char buf[60];
+    char *p = buf;
+
+    while (i < len) {
+        if ((data[i] >= '0' && data[i] <= '9') || data[i] == ';') {
+            *p++ = data[i];
+        } else {
+            *p++ = data[i];
+            *p = 0;
+            j6::syslog(j6::logs::app, j6::log_level::verbose,
+                    "line edit got command: ESC[%s", buf);
+            return i;
+        }
+
+        ++i;
+    }
+    return 0;
+}
+
+} // namespace line